Fix wrong pluralization

The pluralization of the visitors counter in the backend mod status is wrong.

##### Before
![@BUG mod_status before](https://f.cloud.github.com/assets/33978/1353270/ca86b2fc-3742-11e3-9a1d-39379776751c.png)

Note the plural form for `1 Visitors` and `1 Admins`.

##### After
![mod_status fixed](https://f.cloud.github.com/assets/33978/1353267/c5f00766-3742-11e3-9b76-79bd7759b9d0.png)

Descriptions have been corrected and moved to tooltips.