Initial re-write of posts test, bug fixes

Bug Fixes:
General housekeeping to keep all model code as similar as possible.
Decoupled created_at and update_at from id across all models.
Any calls to genId now pass in model.created_at.

Updated the Posts model.js file to handle more ways to generate keys.
Updated the Posts db.js and index.js files to handle retrieving posts by
legacy ids and re-wrote posts.remove to be more complete when removing a
post. (Unnecessary keys are removed)
Updated the Posts index.js file to keep it from leaking the Post model
out to API.

Posts test file now covers more of the post model and interface but a
few more methods need to be added as well as versioning of posts.