Add compass

[rolandlo]

This PR is split off from (and based on) #4211. Only the last commit 96354a9 is relevantcommits from "Add compass" are relevant.

Here is a little demo (mostly using the keyboard; m is for marking the center):

CompassDemo.mp4

Edit: Added demo (Nov 27)

[rolandlo]

After #4211 has been reviewed and merged, this PR may be ready for review.

[rolandlo]

Rebased on master after merging the setsquare refactoring. This is ready for review.

[Technius]

I skimmed through the code quickly, some comments below.

[rolandlo]

Merging in 48 hours if no objections are raised.

[Technius]

I played around with this briefly and noticed a few things:

• This uses the same controls as the setsquare, so that would be nice to note in Add geometry tools documentation xournalpp.github.io#77
• When drawing a line from the center, the line can only extend in length. If the user overshoots, they have to undo the stroke and try again.
• For the center drawing feature, I think it would be better to have a feature where the user can drag from the center to the edge to fix an angle, and then move along the pending line to adjust the radius. This can be left to a future PR, however.
• The following bug affects both geometry tools and can be addressed in a follow up PR: only one arrow key direction can be active at a time. E.g., when pressing both up+right, the geometry tool only moves in the direction of the first arrow key pressed.

These are not major showstoppers, so they can be addressed in a follow up.

[rolandlo]

Thanks for the feedback.

I played around with this briefly and noticed a few things:

* This uses the same controls as the setsquare, so that would be nice to note in [add setsquare documentation xournalpp.github.io#77](https://github.com/xournalpp/xournalpp.github.io/pull/77)

I'm working on it.

* When drawing a line from the center, the line can only extend in length. If the user overshoots, they have to undo the stroke and try again.

It's the same for drawing on the outline of the compass and for drawing on the longest side of the setsquare or drawing on physical paper.

* For the center drawing feature, I think it would be better to have a feature where the user can drag from the center to the edge to fix an angle, and then move along the pending line to adjust the radius. This can be left to a future PR, however.

Interesting idea. It wouldn't allow drawing circular ring (sectors) anymore though.

* The following bug affects both geometry tools and can be addressed in a follow up PR: only one arrow key direction can be active at a time. E.g., when pressing both up+right, the geometry tool only moves in the direction of the first arrow key pressed.

Is that also a bug of moving the page around (without geometry tools then)? Haven't thought about having multiple arrow keys at the same time.

These are not major showstoppers, so they can be addressed in a follow up.