MRTK SDK UX - ObjectCollection (#2606)

* adding abstracted objectCollection -> baseCollection and gridCollection

* fixing re: review feedbacK

* Missed Dave's enum naming suggestions

* pulling out newer changes to ObjectCollection from HTK-master. Various Fixes

* missed the virtual -> abstract fix in BaseObjectCollection

* updating to address feedback

* adding lamdas and a few other fixes

* addressing standards formatting

* fixed a few small bugs when testing & added a demo scene

* added a few fixes that were marked as outdated from a previous commit

* moved scatter to a new collection script, removed type suffix from enum names

* changing all enum suffixes from 'enum' to 'type'

* small formatting fixes

Author: radicalad