Color whole footer background of single-category tasks
Created by: maltehi
Adapted the category coloring to color the whole footer background instead of just the background of the category name as long as a task has only one category. For multi-category tasks, the background of the category name is colored as before and the footer background is colored in light gray.
Compare: https://github.com/evrenvarol/outlook-taskboard/pull/35
Furthermore, adapted the getColor() function to use an array.