musiconhold: Add sort=randstart, and deprecate old stuff.

- adds sort=randstart (next to sort=, sort=random, sort=alpha)
- combines duplicate moh option parsing code into a single function
- adds deprecationwarnings for application=r to sort randomly
- adds deprecationwarnings for random=yes to sort randomly
- removes invisible code that was supposed to stay until 1.8 

The sort=randstart works like sort=alpha, except we start at a random
position.

Review: https://reviewboard.asterisk.org/r/3991/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@423065 65c4cc65-6c06-0410-ace0-fbb531ad65f3