The legend html was not escaped and was ignoring block settings coming
from the form editor.
This commit adds a new helper function for rendering legend that respects
applies block settings and also escapes the output.
[MAILPOET-4471]
Made checkboxes in a form accessible according to the WCAG-standards by adding a fieldset around them and adding a legend describing the fieldset's purpose
(name).
[MAILPOET-4471]