Add option to allow members of whitelisted organizations to whitelist users/trigger PR tests

This adds a config option to allow members of whitelisted organizations to effectively behave like they were entered into the admin list.

Adds logic to ignore bot user comments completely.
Merge pull request #37 from akoeplinger/orgmember-admins

Add option to allow members of whitelisted organizations to whitelist users/trigger PR tests
[maven-release-plugin] prepare release ghprb-1.15-0
[maven-release-plugin] prepare for next development iteration