Item7375: TagMePlugin fails to untag, insufficient and inaccurate documentation

1. If there are more than one users put an identical tag to a topic, one of those users cannot untag the tag
2. On 2013-12-03, the plugin got major enhancements, which has several problems
   1. The two new features, multiple tag namespace and user agnostic tagging, are explained insufficiently
   2. User conscious tagging (the original way) or user agnostic tagging can be specified on the web by web basis even under single tag namespace. Under single tag namespace, user conscious tagging or user agnostic tagging needs to be global since tag search is global
   3. Under user conscious tagging, there is no way to restrict tagging/untagging on any topic. Topic or web owners should be able to restrict who can tag their topic/web
   4. $NO_PREFS_IN_TOPIC is set to true, but still configuration by preferences values are mentioned in the documentation
   5. TWiki::isTrue() is used, which works but is outside the TWiki::Func API
   6. DENY_TAG_CHANGE works as expected only if one group is specified. This is also the case with ALLOW_TAG_CHANGE. In the other cases, they don't work as expected
   7. You cannot specify tag bundles by preferences variable. There is no good reason for that spec

TWiki:Main/HideyoImazu

This also fixes Item6816: User rights for allowing tag delete / rename do not work right.

-- TWiki:Main.PeterThoeny - 2013-11-12