Expanded and revised conditional analysis feature

[abought]

Purpose

We would like to add a way to perform conditional analysis from within locuszoom.

Although an old demonstration existed, it was never fully implemented, and it revealed a number of design limitations in how LZ handles things like annotations. We should unify the demo with new mechanisms, implement calculations, and add several features.

TODO:

• Add a display options button to toggle to display of results
• Fix various UI and alignment issues
• Lock scroll once model building starts
• Add a "suggest best" option that adds the LD ref var to the covariates list.
• Add a UI button to add user-specified variant, or search by various mechanisms.

Summary of changes

• New element_annotation event allows external widgets to respond to annotations (user selected lists of significant points that are remembered across re-render: eg "use this element in a calculation and redraw it with a custom shape")
• [ ] Consider a "custom event" syntax that allows any event to be sent from custom widgets (no longer limit to pre-set event hooks). Example: "calculation complete" can be used to communicate with a data table, and show results only when some defined step in a UI flow is complete.
• [ ] Improve template syntax to support toggles like "add/remove" (#215)
• [ ] Implement conditional analysis calcs in raremetal.js
• [ ] Implement an LZ data source that uses the selected items to drive the calculation

[abought]

On hold until we better define the UI and impact requirements with the T2D portal.