Add MNX metabolite and reaction namespace to DB

[cb-Hades]

To enable faster gap filling, it would be help (and with the current implementations in the GapFiller class even necessary) to include the MetaNetX reactions and metabolites ref and prop files in the database. However, distributing them with GitHub is impossible, as the database becomes to large for the upload.

Possible solution:

Implement an add/update function for the MetaNetX tables, that

• downloads the respective files from MNX
• add these files to the database
• has entry so that it is available both via python import and as a command line function
• Issue: uploading the database with MNX to GitHub not possible - adjusting validation function or separating media and database-connnections-database

Notes:

• implementation can be found in utility.databases and the command access under set_up-> database -> add_namespace | reset
• all four tables can be added to the database