Make bridge descriptor sanitization more maintainable and more modular

SanitizedBridgeServerDescriptor should extend BridgeServerDescriptor. It receives a BridgeServerDescriptor at construction time and sanitizes the descriptor. All getters should only supply sanitized data; this explicitely includes method from the Descriptor interface like getRawDescriptorBytes.

In addition, a SanitizedBridgeServerDescriptorTest should be created that verifies the sanitation and data integrity.