Running training_fill_data_library overwrites bib file

I ran:

```
planemo training_fill_data_library --topic_name chip-seq --tutorial_name formation_of_super-structures_on_xi --zenodo_link https://zenodo.org/record/1324070
```

and it overwrote my bib file with the default + reformatted all of the markdown in the tutorial header which I didn't really want? I'd already changed it there.

Personally I'd prefer that I just supply the tutorial.md file, and it reads the zenodo link from there + updates the data-lib.yml, would make more sense to me.