Allow setting numerical priority

[Yannik Enss]

I use todoman in conjunction with the Nextcloud Tasks app and use all 10 priority levels there.

But if I create a task in todoman I can only choose between 3 levels of priority which makes it impossible to create useful entries without editing in Nextcloud.

[Hugo]

Sounds like a simple change, I'll take PRs addressing this.

I might work on it when I have a bit of free time, but it's unlikely to be soon.