Remove many redundant implementations of canLoadNamedObject()

Summary:
These just got copy/pasted like crazy, the base class has the correct default implementation.

(I'm adding "H" for Herald Rules, which is why I was in this code.)

I also documented the existing prefixes at Object Name Prefixes.

Test Plan: Verified base implementation. Typed some object names into the jump nav.

Reviewers: btrahan

Reviewed By: btrahan

CC: hach-que, aran

Differential Revision: https://secure.phabricator.com/D7785