Fix notification mail template header-body splitting

Since file() doesn't remove "\n" from the lines read the condition
`$lines[$l] == ''` never evaluated to true.
So $mailHeaders would always contain every line from the template while
$mailBody contained none of them.

Together with the bugfix of PHP#68776 [1] disallowing multiple "\n"'s &
preceding "\n" in mail()'s $additionalHeaders arg this caused mails not
being sent because $mailHeaders would include at least one "\n\n" which
was meant to separate the mail headers from the body.

[1] https://bugs.php.net/bug.php?id=68776

See merge request !231

Since file() doesn't remove "\n" from the lines read the condition
`$lines[$l] == ''` never evaluated to true.
So $mailHeaders would always contain every line from the template while
$mailBody contained none of them.

Together with the bugfix of PHP#68776 [1] disallowing multiple "\n"'s &
preceding "\n" in mail()'s $additionalHeaders arg this caused mails not
being sent because $mailHeaders would include at least one "\n\n" which
was meant to separate the mail headers from the body.

[1] https://bugs.php.net/bug.php?id=68776

Fixed language file import problem: https://www.howtoforge.com/community/threads/import-language-issue.70355

FS#3900 - Invalid home dir for shell users. Changed description from -Dir- to -Base Dir- to refelect that /home/username is appaneded to this directory.

Stable 3.0.5 Fixes

See merge request !197

- possible sql injection in monitor sys_state

- Made sure SQL backups from servers that differ from the server where the website is on can be restored. A download of the backup is not possible in such a case, therefore I hide the "Download" button.

- SSH users cannot be deleted if the web site uses PHP-FPM ("userdel: user ssh_test is currently used by process 2890"). Fixed this by stopping PHP-FPM before user deletion and starting it again afterwards.