Style editor scrollbars with light/dark ui theme

Make scrollbars not as jarring by styling them according to the current
ui theme's background and foreground colors
Improve scrollbars styling

Correctly place the border depending on whether the border is vertical
or horizontal. Also made the thumb colors a bit less pronounced
Add info about running npm install and starting grunt in readme

Loading Caret from source requires running npm install and starting grunt to get LESS files processed into CSS.
Merge pull request #101 from elisee/patch-1

Add info about running npm install and starting grunt in readme
Move scrollbar styling to ui.less
Remove scrollbar track border
Make scrollbar track background transparent
Merge pull request #100 from elisee/better-scrollbars

Style editor scrollbars with light/dark ui theme
Hack to fix keyboard for now, but key merges are broken and should be fixed in settings
Many key fixes: mainly that Ace key configs are reloaded from scratch on each init:restart, so that
you can't either wipe out Ace bindings for good, or have zombie bindings hanging around from edit to
edit.
CSS tweaks for visibility on Windows.

Fixes #102.
Fixes #103