Providing provenance information

For reproducibility it would be interesting to have the possibility of obtaining the BridgeDb version and date of execution when performing a mapping.

This could be added to /properties/ in the webservices and/or getProperties() in BridgeDbR

Start by reviewing /properties/ in the webservices and getProperties() in BridgeDbR to understand how mapping properties are exposed. Add a way for callers to obtain the BridgeDb version and execution date, and verify that both values are available through the intended interfaces.

Written by the indexing model from the issue text.