Fix/anonymoususerstats

[TamaroWalter]

Userstats are now fully compatible with anonymous moodleoverflows.
New:

• activity and reputation are divided in "forum" and "coursewide". The forum column shows the activity/reputation for the moodleoverflow, that opened the userstats. The coursewide column shows the activity/reputation from all moodleoverflow from one course. Note that "received up-/downvotes" are only counted coursewide:

• Compatibility with anonymous forum: to guard the anonymity of users, not all interactions in a anonymous moodleoverflow are shown in the userstatistics. This means:
• In completely anonym moodleoverflows (all question and answer are anonym), writing a post, giving a helpful mark or receiving/ up/downvotes won't be counted in the user statistics
• In partial anonym moodleoverflows (only questions/answers from the topic starter are anonym), all activites which affect the topic starter (if the topic starter writes an answer, gives/receives an up/downvote or marks an answer as helpful) won't be shown in the user statistics.