(search) Fix searching tags with spaces

Summary:
Tags containing blank spaces were not handled properly in the search widget.
Now we enclose them in quotes and strip the quotes before setting them to the widget.

Test Plan:
No artifacts when searching tags containing spaces
Added test cases to bin/dolphinquerytest

Reviewers: Dolphin, elvisangelaccio, ngraham, meven

Reviewed By: Dolphin, elvisangelaccio, ngraham

Subscribers: meven, kfm-devel

Tags: Dolphin

Differential Revision: https://phabricator.kde.org/D26369