Add support for Spark in data processing UI

For Juno, Spark jobs will be supported in the Sahara data processing engine. Given that, the data processing dashboard will need some changes to support the new job type.

The corresponding Sahara-api spec can be found at: https://review.openstack.org/#/c/109403/

The anticipated changes are as follows:
* add a new job type for Spark jobs (job creation)
* job launch config screen may have spark-specific fields included or non-applicable fields excluded (tbd)
* help text updated to include spark-specific notes as needed

Update from service side of things: Similar to Java job type. Main is required, but libs are optional. Only used configs (currently) is edp.java.main_class, but can take others [currently ignored]. Can also take args.