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

It seems like there is some kind of touch action interference coming
from the blocks panel, where if you touch the tabs on a touchscreen
chromebook/chrome responsive mode, it does not select the tab if the
touch radius is overlapping the blocks panel at all. See gifs in PR for
more explanation. Fixes issue #1283, making chromebooks useable!

If an extension is loaded at project-load time, there won't be any
targets. In that case, `handleExtensionAdded` now skips target-specific
steps.

This change also adds a filter for JSON block info to support upcoming
block separators, which have XML but no JSON.

Resolves https://github.com/LLK/scratch-gui/issues/1713

Add a jest unit test for making sure the number is rendered out when
provided and not when not provided.

Resolves #1644

Revert "Changes to hash should happen through project loader hoc. Changes to the current project id and current project data should happen in a reducer since they are part of global state. That way, the load button can affect the global project data as well."

This reverts commit e4fe143b.

FWIW the AP style guide recommends "emojis", although many dictionaries
also recognize "emoji" as the plural because that is the plural in the
original Japanese.

Changes to hash should happen through project loader hoc. Changes to the current project id and current project data should happen in a reducer since they are part of global state. That way, the load button can affect the global project data as well.

Remove .sb from file browser filter since we can't support them yet. Remove .zip from the same. Save project as .sb3 (and untitled-project).

scratch-audio depends on sound property being called md5 even though it refers to md5+file ext,
so this property cannot be renamed just yet.

This reverts commit dee7195f.

Added:
- Opera (including Opera Mini)
- Silk

Not Added:
- Vivialdi - appears to be ‘Chrome’ in `platform.name`