This reverts commit 5b9ee9f1, reversing
changes made to bb6c3845.

Newlines were only replaced with <br>'s in the mail body, but not in the configured layout for this mail. This resulted in missing newlines in the layout (everything was more or less in one line).

- Fixed PHPDoc
- Fixed the runtime template cache
- Fixed coding styles
- Changed preg_match to strpos for better performance

- Added static runtime cache

This commit fixes FileReference attachments of multiple consequtive mails
that are sent via the mail queue, for example via the forms finisher with
a user and an admin mail, where files need to be attached to both mails.

Fixed:
- preview markers in the newsletter
- keep values in the newsletter form after sending
- fixed pagination performance in MailQueue