Improve accepting of Socks5 bytestream requests

Implements accepting a Socks5 bytestream request.

• Target tries to connect to each Socks5 proxy provided in the Socks5 bytestream request using the Socks5Client
• every connection attempt now has a time limit to be able to answer to the request before initiator times out
• timeout behavior can be configured before accepting the request
• bad proxies are blacklisted
• target now replies with the correct error if request has to be canceled because of an error or if all connections to proxies failed (http://xmpp.org/extensions/xep-0065.html#usecase-alternate 5.2 A 3)
• #accept() returns Socket to be used for bidirectional use (was InputStream in old implementation)

• tests for handling incoming Socks5 bytestream requests
• handels all cases mentioned in the XEP-0065 (http://xmpp.org/extensions/xep-0065.html#usecase)
• adds Util classes to test implementation without a real XMPP server by mocking the Connection and predefining answer packets

related to SMACK-239, SMACK-169