Added getRelationships function for two users

Changed inRelationship function to a boolean wrapper around
getRelationships
Added relationship ManyToOne association from Messages to
UserRelationship.

Added a setter for relationship
Added messages OneToMany association between UserRelationship and
Messages.

Created addMessage function to add a message to a relationship
Changed the createAction path to /messages/send as it makes more sense

sendAction now adds a relationship to a message and the message to the
corresponding relationship.

latestMessages action is now a GET route called /messages/inbox

inboxAction no longer has a hard coded 50 message limit

inboxAction now uses relationship_checker rather than it's own query
Fixed bug where incorrect errors were reported in indexAction
Implemented deleteAction that removes a valid UserRelationship when
given an id number of a user.
inbox is now only requested when valid user id is selected

inbox is now polled every 3 seconds until I get long polling working