Add Plugin spec

[cromefire]

No description provided.

[heyhippari]

Do note that there is 4 known plugin types right now:

• mediaplayer
  Handles playback for an item type and, optionally, specific items
• preplayintercept
  Has the ability to act before playback starts for some items. It's what handles the warnings when playing ISOs, for example.
• screensaver
  Handles the sources for the various screensaver (photos, logo and so on)
• skin
  This is the one we know the less about since there is no existing instance of it in code.

[cromefire]

And I guess everything besides name, id, type and priority is mediaplayer specific, right?

[cromefire]

Also I hope you are okay with me copying your descriptions into the docs

[dkanada]

The other two we know about have hook methods if I recall.

[cromefire]

Yeah if you got some samples I'd like to add them

[cromefire]

Added all the plugins as plugin subinterfaces