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
Merge branch 'master' into adobe-jasonsanjose/extension-install-draganddrop

Conflicts:
	src/styles/brackets.less
code review comments
Merge branch 'jasonsanjose/extension-install-draganddrop' of https://github.com/adobe/brackets into jasonsanjose/extension-install-draganddrop
Merge pull request #8166 from adobe/jasonsanjose/extension-install-draganddrop

Drag and drop local zip file install for ExtensionManager