Integrate login with moodle

An approach to integrate Q2A inside moodle, so the user logs in to moodle and get automatically logged in Q2A
![integrationmoodleandq2aauthentication](https://cloud.githubusercontent.com/assets/466105/2996615/d4acb38e-dcf2-11e3-9f3f-521523d53f83.png)
![integrationmoodleandq2aauthenticationpluginoptions](https://cloud.githubusercontent.com/assets/466105/2996614/d4abae80-dcf2-11e3-9ead-5462cb708178.png)