Added a cookie hash salt to avoid a potential brute force attack to cookie hashes. The salt has a default value. This salt need to be replaced by the admin.

Configuration file:
server.properties

Configuration Parameter:
# Cookie hash salt to avoid a potential brute force attack to cookie hashes.
# This value should be replaced by any random String with at least 16 Characters.
com.openexchange.cookie.hash.salt=replaceMe1234567 890