[nemo-qml-plugin-calendar] Avoid endless loop when editing event end time.

On handling changes, removing old events required them being
considered less than new event. Inserting new events to an index
required them being less than old event.

When editing ending time of an existing event, neither of the
conditions applied. Thus the loop didn't proceed.
Clean up whitespace
Merge pull request #17 from pvuorela/master

Avoid endless loop when editing end time for an event