Crop enhancements

[Dreamer]

Sometime I need to crop only the bottom part of the screen, so I suggest to replace 2 options (horizontal and vertical zoom) with the 4 options - crop the upper/bottom/left/right part of the screen.

I need the crop especially for one channel, not for the others, so the toggle crop option would be useful for me, as a menu option, keyboard shortcut, and the toolbar button or next to timeshift time. So the crop values would be saved and using the toggle button would just enable/disable it.

More advanced option would be crop option per channel, or a single option in settings:

[x] Use crop for these channels only: [1, 5, 17]

So the field for the number of channels which will be used for cropping.