OO-705: switch the format of pdf's thumbnails to png, implements small admin panel to reset the thumbnails

OO-702: remove the fallback if there isn't any mailing definition, check first the default settings and send e-mails only if it's mandatory

OO-531: fix add to catalog in publish wizard, fix catalog / blog clear cache selenium tests, upgrade arquillian to the last final

OO-687,OPENOLAT-131: make the search in repository case insensitive for the fields author, name and description for Oracle and PostgreSQL

OO-686,OPENOLAT-32: fix enter behavior in wizard, enhance the user search form to accept enter in the autocomplete field and the user attributes form

OO-685: accept comma as separator for float in QTI <=, >=, <, and > test, and prevent red screen if the format of the float cannot be parsed

OO-623: check more places where authors can create groups as enrolment and contact course building block, visibility access rules and course preview form

CL-232: enhance REST API to manage calendar events in a course, hardened login filter against concurrent startup, add headers