disable creating branch from other than master.
Merge branch 'master' into restrict_branching

Conflicts:
	ide/app/lib/git/commands/branch.dart
	ide/app/lib/scm.dart
Add comments.
Merge pull request #2385 from dart-lang/restrict_branching

disable creating branch from other than master.
Improved UX of dialogs
Disable submit button in dialogs when some fields are invalid
Add 'required' attribute to fields that are required (ones with 'pattern' specified)
Merge remote-tracking branch 'upstream/master' into invalid-entries-disable-dialog-buttons
_restoreDialog(), deploy message visibility
Merge pull request #2407 from dinhviethoa/2248-git-dialogs

Improved UX of dialogs
Merge pull request #2405 from cleercode/master

UI styling tweaks
Room for navigation buttons
Merge pull request #2410 from dinhviethoa/tabbar-navigation

Room for navigation buttons
Added new icon
Address review comments

* Remove red text for invalid values in fields
* Use red border only when the field is not focused and non-empty (the user has entered some value in it)
Merge pull request #2409 from ussuri/invalid-entries-disable-dialog-buttons

Invalid entries disable dialog buttons
Fix infinite imports when importing self.
Add todo.
Complete with error instead of thorwing exception.
Fix polymner unbind warning.