Adding event to the middle mouse button click.

This is a continuation of https://github.com/modxcms/revolution/pull/449 in another realization. 
And prevent changes in the current window
Fix unescaped backslash in file and image TV

Fix for #9526: http://tracker.modx.com/issues/9526
http://bugs.modx.com/issues/10267

Content Disposition „Attachement“ -> Filename shows two dots (e.g. file..txt).
bugfix invalid variable on resource/getlist
#747 Fix issue where validation would cause a user's usergroup memberships to be wiped
Update phpthumb to 1.7.11-beta to close security vulnerability

(cherry picked from commit 09e9db207fe83ec4d7fc9794527fd8b2e9aaa17d)

Conflicts:
	core/docs/changelog.txt
Remove cache clearing logic from system setting model

Removes logic in save() and remove() methods of modSystemSetting which unnecessarily cleared the cache. This was redundant as it already occurs in the processors for managing the System Setting records, where the logic is more appropriate.

(cherry picked from commit 1c1d827a3f69b63b47fdd471d5c79fedde0b90c5)
Fix xPDO::getCount() to work with queries containing group by

Closes modxcms/revolution#513
Merge remote-tracking branch 'xpdo/develop' into develop

* xpdo/develop:
  Fix xPDO::getCount() to work with queries containing group by
Merge remote-tracking branch 'xpdo/develop' into develop

* xpdo/develop:
  Fix xPDO::getCount() to work with queries containing group by
Fix unescaped backslash in file and image TV

Merge remote-tracking branch 'origin/pr/615' into pr/615

* origin/pr/615:
  Fix unescaped backslash in file and image TV
Remove extra dot in filename for Content Disposition attachment

Only affects Resources with friendly_urls disabled

Merge remote-tracking branch 'origin/pr/730' into develop

* origin/pr/730:
  http://bugs.modx.com/issues/10267
Fix invalid variable on resource/getlist

Merge remote-tracking branch 'origin/pr/731' into develop

* origin/pr/731:
  bugfix invalid variable on resource/getlist
Prevent removal of user groups after validation fails

Merge remote-tracking branch 'origin/pr/750' into develop

* origin/pr/750:
  #747 Fix issue where validation would cause a user's usergroup memberships to be wiped
Preserve value types in modSystemEvent::output()

Trying to deal with issue described http://forums.modx.com/thread/32541/modx-revo-event-output-issue-in-plugin#dis-post-437548 so now modEvent::output() can be used for setting the output, instead of "semi-private" modEvent::_output, which should generally be used only for internal interactions.

(cherry picked from commit 2e427a5de813d2381bdc5893033e7db960bdbbef)
Add open in new window action to middle mouse button click in trees

Merge remote-tracking branch 'origin/pr/458' into develop

* origin/pr/458:
  And prevent changes in the current window
  Adding event to the middle mouse button click.

Conflicts:
	manager/assets/modext/widgets/core/tree/modx.tree.js