Tweaks & fixes to osx mount PR

I was reviewing https://github.com/rapid7/metasploit-framework/pull/2635, and started tweaking a few things and went a little crazy. Changes include:

* Make PROTOCOL an Enum
* Move path override options to advanced section
* More Enumerable rework
* Move one-off regexes back to inline, pull out protocol list
* Adds some docs to some of the methods to further distinguish the separate sets of shares.
* Allows us to see protocol of Recent Shares
* Parses protocol from file share URL

Let me know if anything seems wrong to you or could be improved. Thanks!