- 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

This commit adds proper error messages when mail sending via the
mail queue has failed. It also refactors the MailTemplateService that it
does not use duplicate code to send mails.