performance

found the performance issue:
Thumbnails where created everytime (the check for existing thumbs was
broken). FIXED!
icon thumbnails

added resizing of post icons.
transparent PNG is not yet supported (alpha is filled with black, see
magic lantern icon)
cache lifetime

added cache lifetime into config. It defines, how ling cachefiles are
valid. If they are older, they are being generated again
style update

just updated the style. Its not yet nice to look at, but i maybe will
someday