thumbnails for the board images

thumbnails are cached for TIMEOUT seconds (django default: 5 minutes)
use board thumbnails instead of bullet points
changed the default thumbnail max-size to 300x80

with a bounding box of 300x80 its more likely that the boards have the
same height, which looks nicer for multiple thumbnails beside each
other.
"Bingo" in headline/title and a link to main page inside the headline
add a full_title block, to allow own game titles
README update.
better text and style for reclaim/create forms.
moved static files to static/bingo.
background image and other style improvements
fix: show the correct board_id on the images.

The correct id is board.board_id and not board.id,
as "id" is the internal id assigned by django,
and "board_id" is the board number on the current site.
better checking for board_id in vote (with ajax)

* use "board_id is not None" instead of "if board_id"
* return an empty response, if neither board_id is set, nor the user has
  a own bingo board.
Order the Boards by "-board_id" by default.

So the user can see in the game lists, what's the latest board, and when
creating a new board, the user's board is at top of the list.
show number of other boards in the "more..."-Link
Option to disable starting new Games
use "pointer" cursor for clickable fields

implemented with javascript, because fields are only clickable, when
javascript is enabled.
renamed get_starttimes to get_times

the function returns end_time, too. So it should just be get_times
fixed TIME_ZONE setting in times.py
fix for end_time at the next day

hour:minute of end_time < hour:minute of start_time_end
means start today and end tomorrow, so add 1 day to the time constructed
from .now()
use timezone.now() instead of TIME_ZONE setting
methods for end_time and the hard/soft expiry time