add videos to playlist from chat

[csandras05]

(Partially) solves issue #262 - adding videos to playlist from terminal (without gui) is still not possible.

[Et0h]

Thanks for the PR.

It might be better if users could add any file to the playlist (as users can when you edit the playlist), which could be useful if they are still downloading the file they were hoping to play.

I've not tested it much, but I think this can be done by making the following changes:

• Remove the various checks in elif command.group('command') in constants.COMMANDS_QUEUE: (within consoleUI.py) and simply using self._syncplayClient.ui.addFileToPlaylist(filename).
• In def addFileToPlaylist(self, filePath, index=-1): in gui.py, replace if os.path.isfile(filePath): with if not isURL(filePath): and replace elif isURL(filePath): with else:

Note: The check in elif command.group('command') in constants.COMMANDS_QUEUE: for if the parameter is blank could potentially be retained, but the other commands do not have such checks so perhaps you should either skip this error or introduce a generic error for a lack of parameter in the other languages for all of the commands for consistency.

Some language issues:

• "No file/url given" - All messages should be in messages_en.py with stubs in other languages (with #TODO: Translate). URL should be capitalised. That said, as above, this error might not want to be retained.
• "\tq [file/url] - add file or url to bottom of playlist", - Should have stubs in other languages. URL should be capitalised.