app_meetme: Use new prompts for administrator menu

The old prompts for the administrator menu were inadequate. They didn't mention
that the menu had additional options through the 8 key and pressing the 8 key
wouldn't reveal what those options were. This patch fixes all of that while
also organizing code pertaining to each individual menu type which was
previously all stored in one gigantic function along with many of the basic
conference functions.

(closes issue AST-996)
Reported by: John Bigelow
Review: http://reviewboard.digium.internal/r/360/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@379885 f38db490-d61c-443f-a65b-d21fe96a405b