Delaying the loading of covers through "guiTickTime" by COT + remove logic to detect the use of the arrow keys

We were doing it by the detection of the up and down arrow keys (5c8d029fcc8d37a8f80c9e9e42550cd38f35e5a0), however it was not efficient for midi mappings.
Cosmetic fixes in wtracktableview - splitting method selectionChange()
New logic to load covers - check if user is stoped in the row for more than 0.1s

It's more efficient because it ensures that we'll only call loadCoverArt after finish quick selections.
Merge branch 'coverArtSupport' of https://github.com/cardinot/mixxx into coverArtSupport_2
Loading cover art in dlgtrackinfo
- It needs more work.
- dlgtrackinfo must handle the cover size and always display them with the same size (scaling).
Checks m_bLastCoverLoaded into an outer if branch

The slotGuiTickTime is updated very often.
Using guiTick50ms instead of guiTickTime

@daschuer: "guiTickTime" is updated after every Audio callback and "guiTick50ms" is the same, but not before 50 ms have passed.
Fixes in CoverArtDAOTest to work on Windows
Loading cover when user open the cover-widget

@kain88-de: I can select a track when the cover-widget is hidden. When I then click the cover-widget I would expect the cover to show. But instead I'm seeing the default cover, I have to another track and back to see the right cover.
Use cover base name as title of the full_size window
Merge branch 'coverArtSupport' of https://github.com/cardinot/mixxx into coverArtSupport_2
Loading default cover art in CoverArtCache
In this way we would be loading it just once and all widgets would get it from CoverArtCache