details response breaking changes

!9 (merged) introduces some breaking changes in the /details response object.

Previously we had 6 different join statements to retrieve every field that had to be returned by /details for the relay type. This introduces noticeable delay and work on the metrics db, causing long wait times for a simple query. To speed things up I've removed a bunch of fields from the details response object:

• exit_addresses
• exit_probability
• middle_probability
• guard_probability
• consensus_weight_fraction

I think it makes sense to create ad-hoc endpoint to retrieve removed fields in order to minimise join statements. @hiro any thoughts on this?