[Feature/Refactor] Refactored mutation observer + changed isUnitsProjElement to isUnitsProjNode which is more general
[Feature/Refactor] update CUs array only on mutations with "childList" changes, otherwise only update any CU overlays
- commented out the code for "grouped" mutations, for now
- event 'dom-muatation' renamed to'dom-mutations' for more consistency/accuracy