Implements Initial lifecycle and App UI start

Closes #2083

* Added hbs template for apps listing
* Added settings to read the activeApps
* Added viewcontrol to activate / deactivate apps
* Added API handler to store activeApps (by `name` in the `package.json` file)
* On button click it turns the button into "Working" and changes class to `button` (grey one)
* On success, rerenders the pane, adds success notification about apps being saved
* On error, rerenders the pane, adds error notification with error message

Missing:
* tests: couldn't figure out how to add mock apps with mock package.json data
* actually registering, etc, re #2140
* icon from the sidebar
Merge pull request #2247 from javorszky/iss2083