gui: PolarOverlay update
PolarOverlay integratino bug fix
gui: PointSelectOverlay fixes and tweaks
gui stream: refactor synchronised acquisition

SEM/AR and SEM/Spec now use the same acquisition code.
Both original implementations are still available, but now used depending on the dwell time.

Still needs more testing... and test cases!
Merge branch 'master' of vpn.delmic.com:odemis