In search - use multiget if server didn't give us the object data

[tobixen]

Ref #115, and depends on #402

Search for TODO: use self.calendar_multiget in the source code.

It's a bit tricky since this needs to be tested with a server not sending us the objects.

[tobixen]

First thing to do here is to create some test in the calendar-server-checker project to see if the server is yielding data or not when a search is done. It's slightly non-trivial as the search()-method already has workarounds catching this issue and loading data. A flag to disable this behaviour could be considered, either that or build the search query and send it to the server without using all the logic in the search()-method