[mediacontroller] add new methods for playlists

[mediacontroller] add new methods for playlists

[ACR]
http://suprem.sec.samsung.net/jira/browse/TWDAPI-239

[description]
added method getPlaylist for interfaces:
- MediaControllerPlaylists
- MediaControllerPlaylistsInfo

[Verification]
tested manually on chrome console
tct-mediacontroller-tizen-tests fails with 2 TC:
- MediaControllerServer_iconURI_attribute.html <- has to be modified,
  because attribute iconURI is no longer readonly
- MediaControllerServerInfo_iconURI_attribute.html <- has to be modified,
  because attribute iconURI is no longer readonly

Change-Id: Idbe3e7f45144574f2dcc799f9e2fc936904c9fff
Signed-off-by: Dawid Juszczak <d.juszczak@samsung.com>