remove empty style tags
use more generic regex to allow possible attributes in empty style tag
add unittests
add another unittest
Improved HTMLUtils::ToAscii, thanks to Renée Bäcker.

Merge branch 'reneeb_htmlutils_avoid_backtracking_to_ascii' of github.com:reneeb/otrs

Conflicts:
	scripts/test/HTMLUtils/ToAscii.t