views description text cleanup

I noticed a few things that needed changing so I made a patch of my changes for you to review.

The changes I made are as follows:
- Changed the description of the 'Twitter message' on the Add View page from "Stores Twitter status messages" to "Twitter status messages" to make it more in line with the other view type descriptions (I thought it could be confusing for some users since views' display information, not store it...)
- Changed the name of the Twitter field that had the help text "The number of users following this Twitter account" from 'Location' to 'Followers'. (copying & pasting error? ;)

NOTE: There are two Twitter fields (in the view) called 'Login name'. I would have fixed this too, but didn't which one to remove and which to keep... Someone else'll have to do this.