fix(INNamespace): correct url for INNamespace#tags()

Previously was requesting /n/<namespace_id>/threads, should be /n/<namespace_id>/tags
fix(capitalizeString): return value from capitalizeString()

Also adds tests which were previously missing.
SQUASH Inflate INFiles from attachment JSON instead of IDs

The API now returns file objects inline instead of just their IDs, so we don't need to resolve them, we can just turn them in to INFiles. It would be preferable to do this when the INDraft/INMessage is inflated rather than by calling attachments()
SQUASH Fixes for JSHint warnings and errors
SQUASH Fix for failing attachment test
SQUASH refact(message): cache reference to self.inbox()
chore(namespace): Converting tabs to spaces