doc: Refactored authentication docs.

I've refactored the authentication documents to separate configuration and bootstrap procedures from day-to-day user managment. I also moved architectural discussions to the architecture paper. There is a link from the quick start guide to User Management. So it should be clearer, easier to understand and easier to use.
The syntax is a little different for each daemon type.

For mon, allow [r][w][x] and allow profile [foo] are the important ones.

The pool and namespace ones are only defined for the osd caps.

The MDS caps are really just 'allow' or blank (not parsed in any meaningful way yet).