User Deposit Contract - allow to configure withdraw timeout

[weilbith]

As the timeout value has changed from block numbers to time in seconds, this has become a challenge for (end-to-end) tests. The current constant value are 25min. That is way too long. In the past we could just mine a couple of blocks. But manipulating pure time is not a good non unit tests.
Therefore it should be possible to set the withdraw timeout in the constructor of the User Deposit contract. This is the same strategy as we already do for the Token Network and Token Registry contract. The deployment tools will then contain the current constant value as the default for the new optional argument.