drag and drop local zip file install for ExtensionManager
refactor install status logic to new Package.installPath() method. add flag to keep local zip files.
UI from @larz0. Refactor from table view to dialog.
revert changed to ExtensionManagerView
use LESS color variables
Dutch language updated (2)

Why it won't work the previous time?
Added missing SHA
Merge branch 'master' into adobe-jasonsanjose/extension-install-draganddrop

Conflicts:
	src/styles/brackets.less
refactored fix from feedback
changed else if to else
fixed fat fingered else error... thx travis
small typo in comment
Redoing the dark theme to be more plain CSS and not rely on central variables.
Update strings.js
Fix inline editor colors.
removed else condition based on review comments
Use correct error message when renaming/deleting folder
Unified error message function, Title cased strings
Use ERR_TYPE_* constants
Consolidate all error dialogs into new method