Issue #192 - Add regId and deviceType in the session model
Fix a typo in the offer model documentation
Add PendingInvitation and InvitationMessage model
Add missing lines to models
Add migration for session , pendingInvitation and invitationMessage
Test the models
Merge pull request #199 from ndomar/Database-Models

Database_Add migration for session , pendingInvitation and invitationMessage