Linking progress indicator for long operations

- Turned `navigateToDeclaration` into a `Future` and return the service call future in `ace.dart`
- Created an analysis bar (toast) to show custom message.
- Invoked progress toast to show after 500ms of analysis activity and hide upon declaration navigation.
- Fixed SparkPolymerDialog.hide() to only hide (was previously showing if dialog was already hidden).

![image](https://cloud.githubusercontent.com/assets/357955/3035219/98e07082-e087-11e3-9b18-6f4b1117f678.png)

I did my best, but I'm sure @dinhviethoa will want to style.

Review @devoncarew @dinhviethoa