Add SlidableLineEdit for integer line edits for slidable value increase/decrease via mouse drag interactions

For more information on viewport-adaptive motion compensation, see:
A. Regensky, C. Herglotz and A. Kaup, "A Novel Viewport-Adaptive Motion
Compensation Technique for Fisheye Video," ICASSP 2021 - 2021 IEEE
International Conference on Acoustics, Speech and Signal Processing
(ICASSP), 2021, pp. 1565-1569, doi: 10.1109/ICASSP39728.2021.9413576.

BETA: Feature block comparison

Implement block comparison functionality comparing motion compensated block if motion is performed in fisheye domain (conventional) vs motion compensated block if motion is performed in perspective domain (reprojection).

See merge request !1

Prototype block comparison feature (compare conventional translatory motion compensated block with reprojected motion compensated block)