2776: Started adding KeepServices model.
2776: Added keep_services model and migration.
2776: Added controller and route for keep_services, fixed tests.
2776: Added Keep services page to workbench (uses default layouts)
2776: Fixed backwards-compatible inclusion of service_host/port/ssl_flag for keep_disks.
2776: Fixed run_test_server.py to work with new 'keep_services' model
2776: Added stub API documentation for keep_services table.
2776: Added 'accessable' route to 'keep_services'
2776: Added test for keep_services/accessable route.
2776: Fixed misspelled accessable->accessible.  Thanks Brett!  Tweaked
workbench icons for keep services and compute nodes.  Removed spurious print
statements.  Tighted up definitions of service_host, service_port and
service_ssl_flag in keep_disk model.
Merge branch 'master' into 2776-keep-services-table
Merge branch '2776-keep-services-table' closes #2776