MDL-40933 Administration: Added 'is after' and 'is before' to date filter
MDL-40320 Course page: Text greyed when conditional activity available
MDL-40889 prevent 304 when minimising JS
MDL-41017 improve purify caching

The improvements include:

* HTMLPurifier cache is stored in localcachedir
* allowobjectembed changes are not ignored any more
* the cache keys include revision and all options which makes
  this suitable for local caches on cluster nodes
* unchanged test is replaced by "true" value which should
  significantly improve performance
* removal of purge_all_caches() hack for directory recreation
* comments and coding style cleanup
MDL-40995 simplify minify integration and fix all known issues
MDL-34785 performance improvement with big list of courses
Merge branch 'wip-mdl-40933' of git://github.com/rajeshtaneja/moodle
Merge branch 'wip-MDL-34785-master' of git://github.com/marinaglancy/moodle
Merge branch 'w32_MDL-41017_m26_purifier' of https://github.com/skodak/moodle
Merge branch 'w32_MDL-40995_m26_minifyreworked' of https://github.com/skodak/moodle
Merge branch 'MDL-35981-master' of git://github.com/damyon/moodle
Merge branch 'MDL-40320-master' of git://github.com/sammarshallou/moodle
MDL-35927 filepicker: add aria attribute to display modal error
MDL-38851 javascript: Full screen dialogs on small screens

This change adds support to M.core.dialogue for showing fullscreen
dialogs on small screen sizes. There are 2 new configuration values that
can be set to control this when creating a dialog (responsive and responsiveWidth).

Setting responsive to false will disable this functionality completely (old behaviour).
Setting responsiveWidth controls the screen width that the dialog will switch to
fullscreen mode. Try not to think of the device that will be accessing the dialog,
but the width at which the content of the dialog needs to be displayed differently.

The activity chooser and the filepicker are the two dialogs that have been converted
in this patch. The filepicker first had to be converted to use M.core.dialog and not
Y.Panel.
MDL-39851 forms: Convert filemanager popups to M.core.dialogue
MDL-39851 filepicker: Fix for toolbar display wrapping on small screens
MDL-39851 M.core.dialogue: Various fixes

Items addressed
* Get rid of custom attribute srcNode
* Change extraClasses to a config only parameter.
* Change attribute fullscreen to a method.
* Restore the original window overflow value.
* Use setStyles instead of setStyle for performance.
* Tinymce end the zindex wars
* Prevent fullscreen dialogs in an iframe (tinymce managefiles plugin).