update databse - strict_mode compatible (https://www.howtoforge.com/community/threads/email-warning-after-modification-of-spam-level.76247/)

Introduced new -processing- state for remote actions. The -processing- state is set by long running background actions to allow the action procedure to proceed with the next action.

First part of fix for issue #3896 - Unknown column 'default_mailserver' in 'field list' when saving client limits main template

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)

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