Simplifies docstring of do_search() in Controller.
Updates docstring of get_entries() in Model.
Some refactoring in get_entries().
Updates docstring in extract_entries().
Updates docstring in search() in Model.
Refactoring in extract_entries() in Model.
Fixes bug in search that only showed the same entry over and over.

Only one TroveEntry instance was initialized in the method which is
plain wrong. There have to be several of them in each iteration of
the loop. Now the search results are displayed correctly.

I will not write a test for this for two reasons:
1) The TroveEntry objects will be removed in an upcoming commit
   to be more flexible and have configurable keys.
2) It is hard to test the positional change of this instantiation.
   The only way I could think of is the concrete example of e.g.
   two entry objects that are written to a test encrypted file and
   a search that will then go through the loop and a counter that
   makes sure that more than one object has been created.