Plugins are now disabled at startup time unless there is some relevant
configuration in hydra.conf. This avoids hydra-notify having to do a
lot of redundant work (a lot of plugins did a lot of database queries
*before* deciding they were disabled).
Note: BitBucketStatus users will need to add 'enable_bitbucket_status
= 1' to hydra.conf.
Respects <slack> blocks in the hydra config, with attributes:
* jobs: a regexp matching the job name (in the format project:jobset:job)
* url: The URL to a slack incoming webhook
* force: If true, always send messages. Otherwise, only when the build status changes
Multiple <slack> blocks are allowed