Added support for FTDB torrent provider (frenchtorrentdb)

Hello;

I added support for FrenchTorrentDB as a torrent provider.

Sadly, FrenchTorrendDB has a login security and we need to use JavaScript to decrypt a token before any login attempt. For this I use the [PyExecJS](https://github.com/doloopwhile/PyExecJS) package. That makes 2 conditions for this provider to works:

* the PyExecJS package (`/usr/local/sickbeard-custom/env/bin/pip install PyExecJS`)
* a JavaScript runtime installed on the system (Node.js works fine)

Far from ideal, but it works. If anyone has a better solution I am open to any suggestion.

PS: I am not a python developer, so this provider is strongly inspired from t411.py and any improvement advice is welcome.