This commit redesigns the jobserver to be based around an architecture
of "workers", which carry out jobs of a particular type, and "jobs"
which are a unit of work carried by a particular worker. It also
introduces "schedulers" which are responsible for scheduling jobs of a
particular type automatically (jobs can also be scheduled manually when
apropriate).
Workers may be run many times, either in instances of the platform
binary, or the standalone jobserver binary. In any mattermost cluster,
only one instance of platform OR jobserver must run the schedulers. At
the moment this is controlled by a config variable, but in future will
be controlled through the cluster leader election process.
* Added initial job server
* Added job server to be ran as part of platform
* Added test job to the enterprise repo
* Fixed job server not loading license
* Renamed job package to jobs
* Fixed TE not being buildable
* Added JobStatus table to database
* Changed fields used by JobStatus
* Added APIs to query job status
* Added config change listener to server
* Added option to run job server from Makefile
* Added ability to enable/disable jobs from config
* Commented out placeholder for search indexing job
* Fixed govet
* Removed debug messages and fixed job api init message
