[jan] Display task list background color in basic view.
Fix link to create sub-task from a task view.
[jan] Add inverse tree icons.
Default external task priorities to normal.
Fix setting task list name for external tasks.
Fix exception name.
Move priority to 2nd column and improve styling.
Improve tickets returned as tasks.

Don't send inompatible priority.
Don't send task list id that requires internal knowledge.
Prefix ticket number.
Use tree and edit icons depending on background. More to follow.