Simplify UserAddressManager

[fredo]

Problem Definition

The class UserAddressManager was moved from Raiden to Raiden-services. We can simplify the UserAddressManager in the following ways:

• no need to store presences from different user_ids for the same address as the PFS only should receive presences from local users anyway.
• no need to search_user_directory
• no need to track presence or whitelist as all users are of interest (or maybe at least all users in the raiden network)