Added all necessary UI hooks for 'bower upgrade'

The actual functionality is still stubbed out.
Small refactoring for better code reuse
Fix the name of bower package installation directory
Cleanups and comments
Merge remote-tracking branch 'upstream/master' into bower-upgrade
Merge remote-tracking branch 'upstream/master' into bower-upgrade
Bower upgrade: 1st implementation complete, but errors out
Fix a bug introduced in previous commit
Working 'bower upgrade'
Fix Bower terminology in UI
Merge remote-tracking branch 'upstream/master' into bower-upgrade
Address review comments: enum type + throw i/o return Future.error
Merge pull request #1724 from ussuri/bower-upgrade

Implement 'bower update' + robust 'bower install'