OO-262: make the default value consistent for the flag "is assessable" of the SCORM course building block

OO-247: make the IM client robust against executor overflow, the changes prevent red screen just after login

OO-244: prevent a rare timing condition if someone logout and open a new browser while a thumbnail is generated (in the real case, the creation of the thumbnail takes 3 minutes)

OO-219 add css markup to better differentiate between done tests and running tests, fix empty table styles