SVN: added SVN Log dialog

Summary:
Added SVN Log dialog. Dialog looks and behaves similar to a TortoiseSVN one.
Dialog supports:
- update repo to specified revision;
- revert repo to specified revision;
- revert file to a specified revision;
- show changes against previois commit;
- show changes against working copy.
Everything is done by the context menu.

{F8181378}

Test Plan: Run SVN Log dialog and check update works, revert works, revert file works, show changes and show changes against working copy works.

Reviewers: #vdg, meven, elvisangelaccio

Reviewed By: elvisangelaccio

Subscribers: yurchor, anthonyfieroni

Differential Revision: https://phabricator.kde.org/D28102