Basic MythTV plugin configuration

Plugin support in MythTV is pretty good, but a little rough around the edges.

1. Add a button to the mythtv project.

   In my case, I added the following block to [mythtv/programs/mythfrontend/library.xml]:

   <button>

   <type>DJ_PLAY</type>

   <text>Start DJ</text>

   <action>JUMP Start DJ</action>

   <depends>mythmusic</depends>

   <depends>mythdj</depends>

   </button>

2. Add a plugin to the mythplugins project.