Phame - create conduit API to create posts

Summary:
nothing too crazy here. try to be smart about some defaults (i.e. phame title is optional and can be derived from title; post as not a draft by default; etc). Fixes T3695.

also do a little re-factoring to centralizing initializing new posts and turning posts into dictionaries. also change blogs => posts in another conduit method so it makes sense and stuff.

Test Plan: made some posts via conduit. testing trying to specify blogger, phame title, and isDraft, all worked nicely

Reviewers: chad, epriestley

Reviewed By: epriestley

Subscribers: aran, epriestley, Korvin

Maniphest Tasks: T3695

Differential Revision: https://secure.phabricator.com/D8485