This commit renames classes as follows:
* TCPConnection --> XMPPTCPConnection
* BOSHConnection --> XMPPBOSHConnection
There are two reasons for this rename. First, it is there to indicate
that the classes actually _are_ XMPP connections, using different
transport mechanisms. Second, it makes auto-completion in IDEs easier,
the developer can type XMPP<complete> and choose the right backend.