update thirdparty/versions.txt
update Changelog.txt and release date
Update Changelog.txt
bump version to 1.6.7
Updated Greek translation.
Some testing on SetAlwaysOnTop. (not working)
PPageExternalFilters: cosmetics.

* Use more meaningful functions names.
* Use correct visibility for the members variables and functions.
Playlist: Scroll and select the latest added item.

This commit fixes #2987.
Playlist: Put MPC-HC on top and give the focus to the playlist after a drag-and drop.