Attach event handlers based on HTML data attributes

[rsek]

Draft to explore a more structured approach to applying event listeners. It prefers data attributes like data-on-click="methodName" so that programmatically relevant data has its own bucket, rather than living with styling information. Practically speaking, that should make it safer to e.g. monkey with CSS classes without accidentally breaking a button.

• standardize naming with function conventions e.g. verbNoun, and make the methods correspond to these
• update changelog
• develop a function (or a class mixin?) to standardize adding "on event, do method()" listeners to be addressed in its own PR

[rsek]

i reckon that i can build on this, but it's quite mergeable as-is, so let's do that. i don't need more long-running PRs, haha

[ben]

I like it. If you've manually tested every one of these changes, go ahead and merge it!