Changed sessions to be saved as a DB.

Added
=====

* New function get_models that returns all viewable models by the
  current user.
* New function get_username that return the name of the current
  user.

Changed
=======

* Sessions are now saved as an sqlite3 database. The DiskStore
  method seemed to have problems when running in "daemon mode".

Fixed
=====

* Fixed bug that caused EOFError when reading session data.
Added schema file for the session DB.
Added new URL for getting current username.

Added
=====

* New controller, account/username that returns the username for the
  current user as JSON.
Added better error handling when launching a job.

Added
=====

* Log error if a launch fails for any reason.
Added session.db to install.
Merge branch 'master' of https://github.com/csdms/wmt