Expiration has changed

Previously, it was 3600 seconds. Now it lasts two weeks.

# 3600 x 24 x 14
imageserver.image_expires=1209600
imageserver.image_cache_control='public'
imageserver.mobile_expires=1209600
imageserver.mobile_cache_control='public'
imageserver.form_expires=1209600
imageserver.form_cache_control='public'