MediaCollectionViewCell: Fix constraints and size

This merge request fixes:

• The MediaCollectionViewCell's conflicting constraints.
• The new label is now correctly shown / hidden when needed.
• The labels' view trailing constraint is now updated when the drag indicator view appears on the cell.

Regarding the Queue View Controller:

• The MediaCollectionViewCell size is now correctly computed, taking account of the labels' font sizes and is not a hardcoded value anymore.
• The thumbnail width is correctly assigned regarding the device type.
• The dark theme is selected when it comes to assigning the colors to the cell model.

Closes #1467 (closed)

Screenshots