OO-1525: update jquery to version 2.1.3, jquery UI to 1.11.4, make the insert line bigger, fix the double event drop events in Firefox

OO-1522: refactor to folder worker poll in a thread pool executor with a very short queue and a CallerRunPolicy to slow down the main indexer if the executor is busy

OO-1522: force writing the index in a single threaded executor which access is blocked to prevent a queue with a lot of big documents

OO-1522: fix an issue where the index are not reloaded after full indexing if Lucene doesn't see that the index has changed

OO-1511: remove relation to assessment mode if a business group is removed from a course, add unit tests

OO-1494: implements rule for group task, tasks assignment deadline and documents submission deadline

OO-1483: implement a prewarm infrastructure to warm-up openolat caches, implement it for velocity templates, display names of users and QTI 2.1 resources