Gitlab individual priorities

[fmauch]

Allow configuring individual priorities for issues, todos and MRs

Gitlab doesn't offer any native priority definition. In the current implementation, issues are prioritized with the default priority, while all other types are hardcoded to have priority 'H'.

This PR lets users configure individual priorities for each, issues, todos and merge requests.

This implements #814

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ToDo's left

• [x] move config parsing to __init__ (https://github.com/ralphbean/bugwarrior/pull/816#discussion_r627878020)
• [x] rename parameters to default_[whatever] (https://github.com/ralphbean/bugwarrior/pull/816#discussion_r627878596)
• [x] Add tests
• [ ] Add to changelog

[fmauch]

Github actions fail for me, but it seems unrelated inside the gmail component: https://github.com/fmauch/bugwarrior/runs/2495725630?check_suite_focus=true#step:5:2367

[ryneeverett]

Also fyi I rebased your branch after fixing the tests and CI.

[fmauch]

I'll continue working on the missing bits (probably over the weekend) and let you know once I'm done.

[fmauch]

I've implemented all I've planned for this. @ryneeverett would you add it to the changelog or should I write a comment there?

[fmauch]

Additional commend: The test for the todo-item is a bit unsatisfying at the moment, as in my opinion todo items don't get parsed very nicely / completely atm. That's going to be the next topic I'd like to address. So, I think it's good that there's a test in place now. I'll write a separate issue about what I think could be improved, just wanted to mention it here.

[ryneeverett]

I've implemented all I've planned for this. @ryneeverett would you add it to the changelog or should I write a comment there?

I'll add a comment on that issue.