Revert "User Ember-Data to communicate with API"

This reverts commit 6054fbedaa9a126c4972fa04c3293d47b603a8eb.

This seems to be necessary since the current implementation of ECG.js
has a bug related to Ember-Data, where adding a new event results in the
study model being in the error state. I couldn't figure out why that is,
and since there is a time pressure, I use the old and nasty, but working
version of a custom data layer :(
Update API calls

So they work with the latest API spec.