Attempt summary doesn't utilize all available functions

Started using this module and I noticed that a number of the functions already built in to the module aren't being utilized. This patch improves the "Attempt Summary" (displayed on the launch page for SCORM activities) by clarifying the language of two functions and implements four more. Instead of just "Total Attempts" and "Completed Attempts," users with the correct permissions can now view "Total Attempts by all users" "Completed attempts by all users" "Number of users who have attempted" and "Number of users who have completed."

Clearly not a huge leap forward, but this is my first patch / attempt at contributing. Would love some review/feedback. Thanks!