Get rid of search "More Options" toggle button

Summary:
With the new compact search filters (type/date/rating) it makes sense to show these options whenever available, and save some horizontal space on the main bar (specially for verbose languages).
These options will be hidden nevertheless if the search is non-indexed or Baloo is disabled.
For some nicer aesthetics D25029 should be also applied.

CCBUG: 386754

Test Plan:
Current:

After:
Along with D25029:

Reviewers: elvisangelaccio, ngraham, Dolphin, VDG

Reviewed By: ngraham, VDG

Subscribers: kfm-devel

Tags: Dolphin

Differential Revision: https://phabricator.kde.org/D25057