Added a new rbintegrations.baseci module, for developing custom CI integrations.

This module can be used to easily build new integrations interfacing with other CI solutions. See the source code and inline documentation for information.

Fixed performing manual CI runs when there are multiple configurations for the same integration.

When using multiple Jenkins, Travis-CI, or CircleCI integrations for automated code review in Manual Run mode, the wrong configuration could be used when clicking Run.

This is now fixed for all CI integrations.