Add configurable JSON location object name and timestamp format for posts from Android and fix references to ActivityType

I ran into an issue when using the plugin, because the request object that I wanted to deserialize to already had an object called location on it.  Providing plugin users with the ability to set an alternative JSON object name (i.e. "mobileLocation" instead of "location", etc) is the solution I threw together.  I ended up wanting a slightly different date format as well, so I later added in a jsonDateTimeFormat option to allow for that.

I also noticed some things that may have been preventing ActivityType from being usable, so I attempted to correct those.