General purpose jobs plugin

This just adds the model layer for creating jobs
Merge remote-tracking branch 'origin/master' into jobs
Add the notion of scopes to the token model
Add progress and log fields to the job model
Make ModelImporter.model static for flexibility of usage
Add utilities in the rest layer for more general tokens
Merge remote-tracking branch 'origin/master' into jobs
Add skeletal job update REST route
Add helper method for creating external job token
Add celery_jobs plugin that schedules jobs using celery

This plugin depends on the jobs plugin and for now just does
immediate job queueing.
Add celeryapp main name as system setting
Fix typo
Whitelist plugins in a gitignore

This will make it so custom plugins that are dropped in will
not appear as outstanding new objects for `git status`.
Allow loadmodel to load models from non-path parameters
Clean up cyclic complexity in loadmodel decorator
More refinement for jobs and scoped tokens
Fix style tests
Add celery user ID setting to celery jobs
Separate job creation from job scheduling

This allows the injection of a job-specific token into the job
payload.
Add utility method for exposing the celery user