move mail template settings to templateeditor repo

fix some minor issues

Added max heartbeat interval to prevent integer overflow 

When using big session timeout values, the interval value might
overflow and cause the setInterval() call to ping the server in a loop
without any delay.

This fix adds a maximum ping interval of 24 hours.

Forward port of 00ec5fc1935c946e846a8ff28491e5b5b017b3d7 from stable6.

Repair broken parent link in the scanner

This reverts commit 482eded8, reversing
changes made to 354cace1.

Added check and cleanup for storage/filecache

drastic speedup for nested ldap groups

fix liskov substitution principle in admin mail template settings

Some tests don't clean up the file cache and sometimes entries are
reused by mistake in subsequent test suites.

This cleans up the file cache and storage after every test suite and
also shows an annoying warning.

Issue/8996 IE8 issues with the new menu 

handle http accept headers more gracefully

Fix #8996