Allow XHPAST lint name rules to be overridden through configuration

Summary:
See T326. Allow lint rules to be selectively overridden, e.g. for Conduit
methods.

Since FB has a long history of suggesting crazy patches for this stuff I think
we're safer just adding a hook class than trying to do some kind of regexp
magic.

Test Plan: Wrote a hook for Phabricator and linted some Conduit files without
issues. Ran unit tests.

Reviewers: nh, jungejason, tuomaspelkonen, aran

Reviewed By: nh

CC: aran, nh

Differential Revision: 874