Improve user experience with eclimd not running

 - GetEclimdInstances: echo in central place
 - Also fix callees of GetEclimdInstances to check its return value.
Fix CommandCompleteWorkspaces: return list and echo
Merge remote-tracking branch 'blueyed/echo-with-no-instances'
consolidate eclimd status checking/messaging into eclim#EclimAvailable

refs #272