Implement new priority data structure. Add color to task list.

Project priorities now follow a similar structure the list and member
JSONs. The priority JSON holds key value pairs where the key is the
priority level (1, 2, 3, etc) and the value is the priority detail. The
priority detail holds a priority label and a priority color.

The task list view now used labels with colored background for a tasks
list, assignee, and priority level. This aids in viewing.