* implement background url support
- Closes#490
* fix lint
* WIP: move input into background picker
* fix cors issue
* keep background select as is
* update UI to select between URL and file
* fetch https url instead of http
* clean up things
* introduce toggle fn
* remove constructor from Collapse (ignore)
* prettier (ignore)
* make Collapse a PureComponent (ignore)
* give ExportSizeSelect a display name (ignore)
* give ThemeSelect a display name (ignore)
* Toggle: displayName, PureComponent, remove constructor (ignore)
* Meta and Slider display names (ignore)
* remove ThemeSelect constructor (ignore)
* fix lint-staged, prettier
* Perf improvements. Limit rerender on keystrokes
* Spread settings props, make dropdowns and carbon pure
* Remove last TODO
* Pass state into value of titleBar input
* Clean up