This commit adds some stubbed data for the pages. The structure of the data
is just a proposal, but it gives the templates something to work with for now.
As a first guess placeholders can be added to messages with the
`((placeholder))` syntax.
This commit adds a Jinja template filter to convert strings containing
said-formatted strings into HTML, which can then be styled to highlight which
parts will be substituted in messages.
Main thing that was missing was including the main CSS file in the template.
There are a few hacky bits here, like moving the whole of toolkit inside the
stylesheets directory.
Would arguably be cleaner using something that isn’t Flask Assets, but that’s
something for later.
