Backport `reactpy_django` features to `reactpy`

[Archmonger]

Current Situation

Currently, ReactPy-Django is significantly ahead of ReactPy in terms of feature set.

While some of ReactPy-Django's features can't exist on ReactPy (mostly due to the lack of a database), a few of them can.

Proposed Actions

The following feature can be backported:

• [x] #110
• [x] #1278
• [x] Convert vdom_to_html to reactpy_to_html
• [ ] #578
• [ ] Support offline HTML fallback within template tags
• [ ] use_query and use_mutation hooks (NOTE: This should probably become an external package)