draggable=false is not enough for firefox

Changed left/right to first/last. Added direction aware styles.

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

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

* removed anything that was made redundant by scratch-l10n.
* updated a string that wasn’t following conventions
* added .tx/config so developers can start updating Transifex when there are new strings

Changed existing string ids to use the convention `<repo>.<component>.<identifier>`

With jscodeshift thank God

* Fix costume loading in sprite info pane

Requires LLK/scratch-vm#517

* Fix costume loading in costumes tab

Requires LLK/scratch-vm#517

Affects SpriteSelector Pane, StageSelector Pane, Stage, MenuBar, Libraries Modal, Add/Import buttons, for Chrome, Ffx + Safari on Sierra.

Fixes #162

Refactored towards better convention for linting.

* Stage/Backdrop: design pass. Changed how selected state works to keep width of pane from shifting. Switched to fixed pixel width to match design spec
* SpriteSelector: removed flex basis width. Pane grows to expand the empty space, since Stage is now fixed width
* SpriteInfo: updated to correct dropdown values. Updated 2nd row type sizing and radio box border-radius
* SpriteInfo: made labels non-selectable. StageArea: added border
* SpriteSelectorItem: Updating type size to match SpriteInfo