Remove already fixed FIXME

Addendum to actual fix commit 0b16c1524b401cdf6c577dd67b3631a520dc653e
fix paster index command usage hint
Fix user activity sorting

Query the solr fields which are actually stored: For the global user
list, this is `order.user.activity`, for instance user lists, this is
`order.user.activity.instance_key`.
Update user activity regularly

As the activity score isn't reevaluated on every user activity, this has
to be done on a regular base - now on a daily base, the same interval as
the instance listings.
fix typos
Add user rating algorithm and sorting (fixes #190)

An algorithm is created which sums ratings user receive for their
contributions. This currently simply adds up the score for user's
comments and the score for the user's proposals rate polls.

This score is added to the user documents in the solr index as separate
fields per instance, as it is done with user activity.

Consequently, the solr score can be used for rating based sorting of the
instance membership lists.