Link interfaces as classes

Summary:
We link classes from extends and instanceof (which can be both interface and class) and from implements (which is always interface).

We don't need to split these two because they share the same namespace.
If we decide to then we will need to:

• Fix DiffusionSymbolController
• Fix repository-crossreference
• Allow more types in DiffusionSymbolController.

Test Plan: Ran the script on secure.phabricator.com, clicked on ArcanistLintRenderer symbol.

Reviewers: epriestley, alanh

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3382