Index UI changes for collections

A few changes are required to make the Index UI work with a large number of collections/indexes:

1. Require at least bucket.scope-level specificity before displaying indexes (default to last-chosen keyspace?). Use the common keyspace control (but with only a bucket and scope level here). This would  restrict the UI to a smaller set of indexes at any given time and takes care of the potential namespace pollution in the UI if we mix scopes on the same screen.

2. Retain the view-by menu. Remove bucket as a selection. 

3. The column currently titled bucket changes to collection.

4. Can the search/filter control work on more than the visible indexes? (Plz

5. RBAC - index list should respect user's RBAC privileges based on scope/collection.

On the indexer side, the /getIndexStatus api is being enhanced to support fetching the indexes for a scope or collection (MB-31937)