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:

UI after filtering:

UI before filtering (smaller edit size):

UI after filtering (smaller edit size):

Reviewers: kfunk, KDevelop

Reviewed By: kfunk, KDevelop

Subscribers: obogdan, kfunk, kdevelop-devel

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