Updates to doc type selector menu on docs home page
Updates to doc type selector menu on docs home page

Fixes [docs-workstream issue #73](https://github.com/rackerlabs/docs-workstream/issues/73)
to improve visibility of Private Cloud docs.

Update doc type selector menu in left navigation to match docs landing
page updates.

- Add Cloud selector filter
- Combine Data and Storage filter

Combined Data and Storage categories to maintain same length for selector
menu.

meker12/nexus-control,rackerlabs/nexus-control,rackerlabs/nexus-control,rackerlabs/nexus-control,meker12/nexus-control,meker12/nexus-control