[Perf/Misc] optimize showOverlay()

Plus, misc small changes
[Feature/Perf] mod_CUsMgr: close #155 (remove code added to handle the complexity arising from having overlay transitions since we no longer have those)

- Plus misc minor improvements
- Some cleanup + possible refactoring still required
[Refactor/Misc] some rafactoring, code cleanup and misc small improvements

Plus, removed some unneeded 'if' checks for early return since they don't seem to be required ever
[Refactor] Refactoring improvements in the code for showing CU overlays
[Refactor] minor refactoring