Templates accessed siteconfig settings through accessing

siteconfig.settings.<name>. However, this didn't handle default

values for the siteconfig.
There isn't a great way of implementing that for templates, so instead,

we have a wrapper that handles defaults, accessible through the

siteconfig_settings context variable. All templates should be updated

to use this instead.
The settings field is also no longer read-only in the admin UI, since

it's now safe these days to modify a JSONField within the admin UI form.

Made use of this in the RB templates, to fix some issues where defaults

weren't provided.