Better keep track of which sets are complete in achievements.

[somiaj]

Store the setID of all completed sets in the globalData hash when evaluating achievements. This allows achievements to use this data vs just counting the number of completed sets. One use case is being able to exclude optional sets, such as review sets, from some achievements without completely excluding them from all achievements.

In addition saving all the setIDs can avoid a double counting completed sets, as there is currently no check to ensure a set is not counted multiple times, and a student can earn the complete N sets achievements by submitting a problem on the same completed set over and over.

This also cleans up some typos in the comments and formats them better.

[drgrice1]

Other than minor code quibbles this looks good.

[Alex-Jordan]

If a student completes a set, and then that setID is stored as completed because of this commit, and then the instructor unassigns/reassigns the set, will everything be working here as expected? I don't recall what's going on with the globalData hash.

[somiaj]

The globalData is stored in the achievements table and is not modified by assigning/unassiging sets. If the set was unassigned, then reassigned, they would still be counted as having completed it if it a set with that id was completed before it was unassigned.

This was also true before this change, unassiging a set that was complete would not reduce the completed counter. Overall achievements are very fragile to stuff like this. This is just a little more robust than before because it won't allow double counting a set even in the case you describe.