Buttons for selecting upper-right or lower-left extent when adding center track

[keller-mark]

Description

What was changed in this pull request?

Buttons for selecting the upper-right or lower-left extent were added to the center square of the add track position pop-up menu. The behavior of HiGlassComponent.adjustOtherTrackOptions had to be slightly modified (https://github.com/higlass/higlass/compare/develop...keller-mark:keller-mark/add-center-track-with-extent?expand=1#diff-77a44232595309f20e1f8787348f2734L3179) to prevent infinite loops.

Why is it necessary?

Not necessary, just an enhancement.

Fixes #759

Screenshots

No hover:

Hover over center:

Hover over upper right triangle:

Hover over lower left triangle:

Checklist

• Set proper GitHub labels (e.g. v1.6+, ignore if you don't know)
• Unit tests added or updated
• Documentation added or updated
• Example(s) added or updated
• Update schema.json if there are changes to the viewconf JSON structure format
• Screenshot for visual changes (e.g. new tracks or UI changes)
• Updated CHANGELOG.md

[pkerpedjiev]

Nice addition! Would you mind adding a section to the docs describing this?

A mention here: https://github.com/higlass/higlass/blob/develop/docs/tutorial.rst
And a more detailed description with a screenshot here: https://github.com/higlass/higlass/blob/develop/docs/views.rst

[keller-mark]

Thanks! I have added some info about this to both of those places.

[pkerpedjiev]

Would you mind adding a quick test to touch this functionality?