Logged-in member viewing member list sees his entry highlighted.

This should close Issue #65.

Two major new bits of code:

1. New `UserDataDecorator#build_index_row_for(post_count)`; takes all
   the stuff that was being explicitly done in the index view to build a
   user-listing row and moves it in here, so that the row attributes can
   change depending on whether the user being reported on is the current
   user. (Takes five lines of template code down to 2);
2. New `member_viewing_member_list_sees_own_listing_highlighted` feature
   spec. Note the (long) setup block, where it marshals copies of the
   user data into and out of an array. THIS IS THE *ONLY* SAFE WAY TO DO
   A DEEP COPY IN RUBY.

RSpec: 636 examples, 0 failures
RuboCop: 148 files inspected, no offenses detected