xbmc: Bad client permission

[jahschwa]

Apparently Kodi disabled GET requests for action endpoints:

• https://forum.kodi.tv/showthread.php?tid=324598
• https://github.com/xbmc/xbmc/pull/12281

Fix is to switch to POST:

• https://kodi.wiki/view/JSON-RPC_API#POST
• https://github.com/TheSchwa/sibyl/blob/8dd893e7b0f671f681703548aed709160bd47dc3/lib/util.py#L68

(09:59:49 PM) user: !audio FILENAME
(09:59:49 PM) sibyl: Unable to open: FILENAME

(11:42:58 AM) user: !xbmc Playlist.Add {"playlistid":0, "item": {"file":"FILEPATH"}}
(11:42:59 AM) sibyl: {u'message': u'Bad client permission.', u'code': -32099}