implement stop and start app buttons in UI

- [x] the buttons are implemented and wired to methods
in app.controller
- [ ] a service needs to be implemented
- [ ] need logic for determining if the app is currently
runnig to disable or enable the buttons

See #166 
@bajtos @anthonyettinger 
I am not a fan of keeping commented-out code. More likely than not, it won't work by the time you will want to uncomment it.

Could you please delete the line instead?