[WMT] Add all wmt
This PR adds all wmt datasets scripts. At the moment the script is **not** functional for the language pairs "cs-en", "ru-en", "hi-en" because apparently it takes up to a week to get the manual data for these datasets: see http://ufal.mff.cuni.cz/czeng. 

The datasets are fully functional though for the "big" language pairs "de-en" and "fr-en". 

Overall I think the scripts are very messy and might need a big refactoring at some point.

For now I think there are good to merge (most dataset configs can be used). I will add "cs", "ru" and "hi" when the manual data is available. 