Devoncarew error checking

Provide better error feedback to users, and log information about our slow tasks.

- add additional error checking to our web and chrome launches
- add the ability to easily notify the user about errors
- show progress when restoring the sync file system
- show progress when compiling a dart file with dart2js
- log information about long-running tasks so we know where the app is spending time
- fix a timing issue where the workspace would not restore itself

@keertip