New design for extended search options

Summary:
Replace the arrays of radiobuttons in dolphin search box to more simple dropdown boxes.
This provides a leaner look, saving a lot user space on the main view and it is more consistent with the 'Search tools' in the most known sites (Google, DuckDuckGo, etc.)
There is room for improvement, as QComboBox doesn't match perfectly with the tool buttons used avobe, but I think it is an improvement over the current situation.

BEFORE:

AFTER:

Test Plan: Same behavior with different aesthetics

Reviewers: elvisangelaccio, Dolphin, VDG

Subscribers: ndavis, ngraham, kfm-devel

Tags: Dolphin

Differential Revision: https://phabricator.kde.org/D24602