* Fix all the little RTL layout bugs

- [ ] borders on toolbox and workspace mirror correctly
- [ ] spacing on stage selector is correct
- [ ] stage size icons are mirrored
- [ ] extension library coming soon text is positioned correctly
- [ ] only mirror blocks icon on the tab (others stay right-handed)
- [ ] drop down icon in create variable modal has correct spacing

* FIx RTL backpack header border-radius

* round the bottom corner of paint/sound editors

This makes the editor’s asset panels match the blocks.

padding and margin changes to make www project page layout work without hacks; hack to position monitors correctly

* Don't show intro modal if hideIntro passed to PreviewModal

* Add hideIntro prop to GUI

* Move intro modal hiding logic into its own function

I think this switches all the icons we saw. I also switched the icons on the tabs (the blocks going the wrong way looked bad).

Correct margins for tabs, tab icons.

Goes along with https://github.com/LLK/scratch-blocks/pull/1646

Fixes #2448 (tab wrapping in Japanese). Also ensures that none of the Sprite info area wraps. Does not address the issue where the sprite info area is too big and pushes the stage info off the screen.

And implement toggle on player playground

I don't love this solution, but I remember not being able to figure out a way to not specify the max width because it is needed in order for the flowing to work. Without the max-width, the sprite tiles try to be in a row, pushing over everything else.

Also remove some obsolete code

Pass a `stageSize` property down from a centralized `MediaQuery` in the
GUI component, and control the size of the stage and all surrounding
elements based on that value. Note that this is a pure property and is
not stored in the Redux state, since we gain access to the results of
the media query during `render()` and we shouldn't change Redux state
during `render()`.

Some stage-adjacent elements don't yet react correctly to the smallest
stage size.

There will probably need to be more backpack config options in the future, so just make this a bit more future proof

* Player mode

Add isPlayerOnly property on GUI. Move isFullScreen into mode reducer with isPlayerOnly.

Full screen needs to be a separate prop so that GUI knows what to show when exiting full-screen (either player-only or full editor).

- set `gui-body * {box-sizing: border-box;}` instead of expecting it to be set by the enclosing component/playground, and removed uses of content-box (adjusting sizes as needed) 
- Added `!isPlayerOnly` to the conditions for draggable sprites
- rewrote player example to use player mode.

This reverts commit 29d5619d.

* WIP tips

* WIP first card stack

* WIP use tips reducer to show things to try

* single card deck similar to mask sequence

* collapse option

* Add zoom card

* WIP tips

* Reorganized to redux

* Add zooming to the gifs

* Blue cards + navigation

* Add tips to new nav bar

* Remove blue

* Update design with icons

* deck updates wip

* Updated card decks

* Add videos to libraries

* Update initial card and clicker preview

* Add backdrop to initial card step.

* WIP use vimeo player instead

* New simple spin deck

* Spin around and say hello decks

* Update button and sub-card styles

* Fix "tips" button in menu bar

* Use move cursor

* Fix cursor

* Use same image for deck preview and library

* Fix cursor again

* Update clicker game deck

* Add videos as single-step decks

* Change tips in menu bar to ? icon

* Change “tips” to “how-tos” in library

* Add help icon to cards

* Update deck library images

* Add drag cover for youtube video to prevent catching mouseup

* add a step to spin deck for clicking control

* Blue bar style updates

* Add step pips

* Update clicker game name to run away

* Fix image padding

* Add change color step to spin deck

* Add start sound step to run away deck

* Update say deck to start with adding a sprite

* Remove package lock

* Remove zooming functionality

* Remove unnecassary prototype changes

* Split up rendering of cards into smaller parts

* Use FormattedMessage for all strings

* Automatic lint fixes

* Almost finished with lint errors!

* Fix more lint errors

* Clean up CSS

* Fix webpack config

* Updates to preview modal for release

* Design tweaks and remove import modal

* Resolve issues with tests

* Copy edits HT Eric

* Resolve lint issue with integration test

* One more change to the disclaimer language

* Add line break

Updates include modifications to interaction states for the following: tabs, add menus, forms, and stage selector.

- Auditing color CSS and componet CSS to make consistent.
- Made a first pass of changes to increase contrast to elements that previously were problematic