Feature/new interface integration part8

* Makes page loading smoother
* Implements track deletion with confirmation only for existing tracks
* Adds error messages on submission failures

(Remake of #85 with merge target develop due to merging of  feature/new_interface_integration_parts 5 - 7)

Could this be structured a little bit differently for conciseness/readability?  It could just be that I have a personal preference against empty returns, but I think this could work:
```
if (track[id] && $window.confirm(...)) {
   // post to delete
   // splice the result set
}