Change order of new-item delete/save buttons

Otherwise the delete button of a new column is not nicely aligned with
the delete button of existing rows
Add plugin-details template hook
Add CSS to style code boxes (e.g. shell commands)
Improve i-form margins a bit
Give plugins more control over asset injection
Handle checkParams returning a redirect response

That way we don't need to use the old _redirect() or doProcess=False
Fix for collapsable table details