Use new loopback app features - app.restApiRoot, "start" event [DO NOT MERGE YET]

Requires strongloop/loopback#123
Relates to strongloop/loopback-workspace#34

Note that the "start" event is not emitted by loopback app yet, the change will be implemented in a pull request for loopback-workspace (coming soon).

We need to bump up the minimum loopback version in package.json before merging this change.

/to: @ritch 
/cc: @sam-github