feat(ionContent): use child scope instead of isolate scope

Adds new '$ionicBind' service, which takes an object containing
binding definitions (similar to angular directive isolate scope
definition).  Allows binding of any directive attribute & expressions
from a scope, letting us do normal attribute -> scope binding
without having to create isolate scopes.

Closes #555. Closes #669

js/ext/angular/src/ionicAngular.js

@@ -3,6 +3,7 @@
  * modules.
  */
 angular.module('ionic.service', [
+  'ionic.service.bind',
   'ionic.service.platform',
   'ionic.service.actionSheet',
   'ionic.service.gesture',