Update datasources.tsv

[DeniseSl22]

There are quite some outdated/deprecated example mappings in the datasources.txt file.
Several issues have been filled on that matter:

• #3
• #4
• #8
• bridgedb/BridgeDb#15
• #7
• bridgedb/BridgeDb#33
• bridgedb/BridgeDbWebservice#29
• #6

So, time to clean up that mess (perhaps make a "deprecateddatasources.txt file, to keep track?).
@egonw suggested to test the linkouts automatically to see if they resolve.

[ariutta]

A semi-related issue: datasources.txt vs. datasources.tsv.