Excel export of paid users and a quick fix for user being allowed to "change history"

### In resonse to email from L.E.G.K this morning:
Adding view that returns exported excel file with all paid users for any given LAN. I suggest someone better at design make a button somewhere :)

### Also:
Should close #75 as users are no longer allowed to unattended lans that have started, and no longer allowed to attend lans that have ended.