Deduplicate regex
Remove superfluous python-format
Whitespace
Line length
Do not overwrite the icon 0 in custom messages

It does not exist yet, but this would be a great opportunity for weird
bugs should somebody ever decide to add such an icon.
Fix outdated documentation
Rename `type` to `msg_type` for consistency reasons
Do not imply misleading `size` attributes for AutoResizeContainer

These would only make sense for empty containers, which these templates
are as far from as possible.