Changing default confidence threshold for new detectors from 0.9 to 0.75

[timmarkhuff]

This PR changes default confidence threshold for new detectors from 0.9 to 0.75.

The rationale is:

1. the web app uses 0.75, so we should be consistent
2. 0.75 is a more reasonable default, and trying to get started with a detector that has a confidence threshold of 0.9 can be painful because there are so many escalations.

I updated public-api.yaml and then ran make generate to update the necessary files, according to the instructions in DEVELOPING.md.

[brandon-wada]

I forgot, changing the public-api.yaml is the reason we didn't do this sooner. This is fine, but this is the Absolute Last time that anyone should manually edit the public-api.yaml file

[robotrapta]

This should bump us up to 0.16

[robotrapta]

I think this classifies as a "breaking change" functionally speaking - in that client code will not behave the same after the change. So I think that means we should bump to 0.16.0

[timmarkhuff]

Done.

[timmarkhuff]

I forgot, changing the public-api.yaml is the reason we didn't do this sooner. This is fine, but this is the Absolute Last time that anyone should manually edit the public-api.yaml file

Okay, at some point you'll need to teach me what the alternative is :)