8337b7ec1 fixed a regression in the Reactified tag selector that
prevented it from using GTK theme background colors on Linux, but it
accidentally made the background gray by default. This restores the
default white background.
Fixes#1684
- Don't cut off bottom of tags on Windows
- Fix appearance of search bar on Windows/Linux
- Fix cancel button on Windows/Linux
- Don't cut off right-hand pane of bottom bar when narrowing pane
- Added icon-button UI code for the menubutton
- Upgrade to React 16 to allow non-standard attrs, such as `tooltiptext`
to support XUL tooltips
- Add i18n support for React UI elements
- Update tests for reactified tag selector