Tracking optimization 1

Faster tracking, achieved through pre-allocation of images and drawing a
smaller window.
Re-centering while tracking has been implemented
Added features to tracking

- It is now possible to stop tracking with pause button
- It is now possible to edit a previous track by selecting a 'tracked
cell' it after pressing the start/stop track button.
- It is now possible to save the annotation structure
- Manual thresholding bug was corrected (filling space when there was
not an object in the selected coordinate).
- It is now possible to inspect previous tracks by selecting a 'tracked
cell'.
- Added a centering button to find set the origin where currently
selected cell is visible.