feat(compiler): gracefully handle empty lists
feat(directives): $cssUrl
Implemented directive scoping

Directives can now declare their controller visibility (local,
children, direct children) via $visiblity static fields.
Disabled implicit injection on the injector.
Depends on https://github.com/vojtajina/dart-di/pull/7
Style, typo and iit fixes
Added explicit dependency on https://github.com/pavelgj/dart-di.git behaviors branch
Merge branch 'directive-scoping-di-dep' of https://github.com/pavelgj/angular.dart into directive-scoping-di-dep