Add mapping from groups in crowd to roles in wordpress

Hi, I added fourth login mode, that enables the user to map groups to roles, for example

* **Joe** is in *crowd* group **admins**
* **Bob** is in *crowd* group **writers**

There are mappings in wordpress:

* from **admins** to **Administrator**
* from **writers** to **Conributor**,

then, when the users log for the first time, they get assigned the role based on the mapping, that the admin of wordpress set in the plugin administration. For this example, that means, that 

* **Joe** will be **Administrator**
* **Bob** will be **Contributor**

I also formatted some code along the way.