Add filtering for ProblemsView

Summary:
The patch adds filtering UI for ProblemsView which is useful when we have a lot of problems - for example select Parser problem model and activate "Current Project" scope for big project (like kdevplatform).

BUG: 339839

Test Plan:
Tested on master branch.

UI before filtering:
{F370200}

UI after filtering:
{F370201}

UI before filtering (smaller edit size):
{F370252}

UI after filtering (smaller edit size):
{F370251}

Reviewers: kfunk, #kdevelop

Reviewed By: kfunk, #kdevelop

Subscribers: obogdan, kfunk, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D3108