frontend: added proper "Tournament is Running" page

This was not deemed necessary before, because you usually were not fast enough to reach the page manually, since the tournament execution took only half a second or so. However, it appears that the production server will be much slower. Meh.
frontend&backend: changed a lot of text; added possibility for user to set tournament execution count; minor tweaks
backend: cache only tournaments with a run count > 10
frontend: tournament page: adjust info text in "Group Phase" column slightly
made home-advantage rule default active again
added site "Technical Details" that briefly describes the simulation process and the rules