R1:95a99e71c6f1

Require Conduit methods to be instances of ConduitAPIMethod

Test Plan:
Deleted `extends ConduitAPIMethod`, then:

$ echo '{}' | arc call-conduit conduit.ping

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4190