Implements a colored background if bind fails to load the zone due to errors
Implements a status text if errors occured
Implements not removing a zone if errors occur. instead old zone stays loaded

This Checkbox can be enabled or disabled by template.

Further I fixed an inconsistent design (HTML) which was introduced by @tbrehm yesterday I tink. (DKIM-Checkbox)

- hooked ssl and ssl_letsencrypt checkboxes

- added limit for letsencrypt and directive snippets selector to client limits
- hide ssl tab if letsencrypt is selected