Track view should support a compact display mode

[fossfreedom]

from #281

The currrent track view takes its entry display columns from the library view.

However - I'm often only interested in the track number, title & track-time. Since I do have a few compilation albums - where an album has more than one track artist, the compact mode will display track number, artist, title, track-time

Thus I'm going to implement a compact mode (by default) - a toggle icon next to the ratings widget - toggle on being display full entry view as now. This also has the advantage to free-up the space on the right hand side of the track view so can display the full album cover here as per the iTunes screenshot

Note: the image should resize automatically depending upon the entry view size - this Q&A should help:

• http://stackoverflow.com/questions/12364112/how-to-do-automatic-image-resizing-in-python3-with-pygi

[fossfreedom]

To do list:

1. connect draw signals after the model has loaded - this will speed up loading
2. Change from GtkNotebook to GtkStack. This will free up 1 1/2 lines space
3. Add the GtkStackSwitcher as first element on left. Rating must be in the middle. Compact/Full toggle on the right.
4. code cleanup - remove all the commented out stuff

Later - lets investigate more if we can remove the custom draw - need to investigate wrapping the GtkImage with a GtkScrollWindow to control the sizing. If this is possible, then can then use GtkStack to give animation when flipping between coverart. - EDIT - custom draw removed

[fossfreedom]

noticed sometimes that when making the pane smaller the buttons at the bottom disappear off the screen - looks like the image gets stuck at a certain size and no longer shrinks. Need to investigate - reopening.