Remove empty statements
Enable PacketExtensions for IQs

This is actually only part one, i.e. with this commit if the user adds a
PacketExtension to an IQ it will be included in IQ.toXml(). Which was
previously only the case if the IQ subclass explicitly included packet
extensions.

The second part of the change is to change the IQ provider, so that
packet extensions are automatically parsed.

Cases where PacketExtensions are used for Message and IQ are slightly
changed. The IQ sublcass now only has a field with this
PacketExtension (see for example
bytestreams.ibb.packet.DataPacketExtension).

Also changed hoxt API: Removed unnecessary indirection and made the
API more Smack idiomatic.
Message Evenents is in smack-legacy and documentation/legacy
Don't use extending stanza addressing if not strictly necessary
Apply builder pattern to ConnectionConfiguration

Introducing a clean split between the constant connection configuration
parameters, which are now all in ConnectionConfiguration and the dynamic
connection state (e.g. hostAddresses) which are now in
AbstractXMPPConnection.

Also removed all arguments of login() since the username, password,
resource and callback handler need now to be configured via
ConnectionConfiguration.

Also remove documentation/extensions/messageevents.md, as it's already
in documentation/legacy
Add reply timeout to NoResponseException message
Fix END_DOCUMENT handling in XMPPTCPConnection

The 'break' statement in the END_DOCUMENT case should break the parsing
loop and not the switch/case within. Therefore we need to add a loop
label on break on that label.
Throw a NotConnectedException on disconnect()

if not connected. For consistent behavior, so that it is always
thrown. Previously it may be thrown or not.
Implemented MD5 just like the SHA1 util