[mythtv] Updating the wiki

[Peter Bennett (cats22)]

I have been looking at the mythtv wiki and how to keep it up to date. I
see two main entry points: "Official Documentation"
(https://www.mythtv.org/wiki/MythTV-HOWTO) and "User Manual"
(https://www.mythtv.org/wiki/User_Manual:Index). I think the "User
Manual" structure make more sense. It could be expanded and perhaps a
category of "User Manual" could be added to make the index page easier
to manage.

Some pages have the notation "This page is up-to-date to MythTV version
0.21, the current release is 0.27.5", e.g. User_Manual:Initial_Installation.

In the official documentation it has Document conventions, including a
"Plus sign" Icon for "Add.png Feature that has been added to git (a
distributed version control system) but is not available in the current
release". I propose to use this icon with the notation "Since 0.27" to
indicate a feature that is available since a specified release. Where a
future release (e.g. "Since 0.28") is indicated the feature is not
available yet. This could be used throughout so that we could start
adding documentation of 0.28 features to the wiki before 0.28 is
available. Entire pages could also be noted that way, by putting the
notation at the top of the page.

This way we do not need a new "Official Documentation" page for each new
release. Also if we introduce something new in release 0.27.5 it can be
so noted.

If we create templates for the "since x.xx" notations, we can use the
wiki to find references to those templates, and that way get a list of
features documented for each release.

"Official Documentation" is one huge file - I think it should be moved
into the "User Manual" and split into smaller topics.

The User Manual contents which is at the right of user manual pages, is
a manually update list of links. It would be nice if that was
automatically generated. I am new to media wiki, I will try to figure
out a better way of doing it.

Peter