Questions:
* should the message strings include the number? Or should that get added to the name when the name is defined
* added a new ‘shared-messages’ to handle the definition of backdrop, costume, etc which are used in multiple places, they’re all related to defaults, so should it all be in `lib/default-project`

styling for title field; correct input target in tests; make download filename safer with default, max length; in playground index, correctly pass props through to gui container

/ht @chrisgarrity

Removing this was the point of moving the test up one level. Thanks @chrisgarrity, good catch!

If the VM is ever instantiated, which happens whenever GUI is instantiated due to default props, then IE11 will crash

Just use ProjectLoaderHOC to translate props to redux. Trying to be clever about using both props and redux state together was... not clever.

Resolves #3040

Fastly is not configured yet

Unfortunately I couldn't do the same with loading projects, since the presence of the component (necessitating the menu to be open) allows the actual upload from file to work, since it needs the FileInput component to be present, so it can emit a change event.  We should revisit

fixes #2983

* 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.