Upgrade community/collection tree browser component

Customized frontend solution to community/collection tree browser. This solution follows dspace-angular component and asynchronous data fetching designs. In doing so, it is not capable of fully expanding the entire tree at once.

Version 7 issue: https://github.com/TAMULib/dspace-angular/issues/14
Version 7 PR: https://github.com/TAMULib/dspace-angular/pull/48