Style & Functionality update. =]

Ahoy!

* recolored the pitch. Looks a bit more realistic colored white (#EEEEEE) than grey :wink: 
* Empty names are disallowed as new player name, mostly because it won't be changeable if changed to "" (empty) or "    " (space-filled).
* Players are now dragged! That means you get a live update whilst moving a player.
* `SITE_DOMAIN` from `settings.php` is now blank: that means that all links in the project are relative (it's dynamic! :sparkles: ) plus the project works out of the box. :package:
* Player labels are now placed into a small, round box with half-transparent background. Looks good, imo. :blush: ... and when hovered, the transparency changes. Small CSS3-Transition. :smirk:
* Player initial position is now a bit left, next to the pit.
* Fixed `save-lineup.php` as it redirected me to error.html, no matter if it worked or not. As said, fixed. (1d29b305f3e38d1c22e5345e3ce745977ca02a38 for more info.)

... thehe. :blush: