Add trait ontology export in obo format

[bellerbrock]

Expected Behavior

To complement the obo loading script, it would be very useful to be able to export a database's trait ontology in obo format

For Bugs:

Environment

Steps to Reproduce

[lukasmueller]

This requested by BI OnRamp (Keo)

[chris263]

I am turning this ticket to "Critical" because there are few databases with missing obo file. This feature will be very important to solve the problem.