Deferred static files

[Archmonger]

This PR adds a static_css component, which reads the CSS file's from disk, stores the contents in cache (for performance purposes), and then puts the file contents into a html.style tag.

Currently, IDOM has no real way to "wait for CSS to load". This will lead to visual jank when attempting to use html.link to defer load CSS loading until a certain component exists. For example, visual jank occurs when using

html.link({"rel": "stylesheet", "href": static("conreq/buttons.css")})

This also mitigates the need for the following (within Django only):

• IDOM Component: Deferred Loader reactpy#725

Changelog

• Deferred static file components
• Docs for deferred static files
• Bump minimum IDOM version
• Create PR templates
• Sync issue form template with idom-team/idom
• Pin selenium to 4.2 for compatibility
• Bump django-idom to v1.1.0
• Docstring for component template tag
• Minor readme wordsmithing