Initiatives: implement "cooked HTML" template parsing

[Beanow]

Depends on #1417
This plus the #1480 PR replace the previous #1418.

Will return a partial Initiative, or throw when the template isn't matched.

Based on the template that's currently used on the forums:
https://discourse.sourcecred.io/t/about-the-initiatives-category/242

[Beanow]

Missed the "considers blank status incomplete" test from previous code.

[Beanow]

@decentralion @wchargin something weird going on with sharness here.
The ":(exclude,top)src/plugins/initiatives/htmlTemplate.test.js" exception is required to make a local yarn sharness or yarn test --full succeed. But the CI test passes without it.

[Beanow]

Switched the DOM parsing to be synchronous. As the implementation is also synchronous, just supports streaming data if needed.