Add indexes to statistics fields

[jde]

Index the sorting criteria on the user_statistics table:

statistics.comments.all.all.count statistics.comments.all.all.replied_count statistics.comments.all.all.replied_ratio statistics.comments.all.all.reply_count statistics.comments.all.all.reply_ratio statistics.comments.all.all.word_count_average statistics.comments.all.ModeratorDeleted.count statistics.comments.all.ratios.ModeratorDeleted statistics.comments.all.ModeratorApproved.count statistics.comments.all.ratios.ModeratorApproved statistics.comments.all.CommunityFlagged.count statistics.comments.all.ratios.Communityflagged

statistics.actions.received.likes.count statistics.actions.performed.likes.count statistics.actions.received.flags.count statistics.actions.performed.flags.count