OO-1926: added formaDateRelative to formatter to add a specific period of time to a baseline date and format it short. made it available in the phantomJS certificates
OO-1914: if the SCORM resource in a course element is missing, show a message instead of a red screen.
OO-1898: email send to external service can be (or not) templated, the registration email will be templated if the content is in HTML format.
