(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.

{F7854247}

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