Added priority feature

I've adde a priority feature so you can type c+tab h+tab l+tab for critical high low priority. I've choosed this priority because "critical" has more chars than "high" and "high" has more chars than "low" so you have the evidence of a bigger color label for high priority task.

I've also modified al themes to have the coloring in all cases
If there are no reason, please fix it and add note in readme and tutorial, then I’ll merge.