Reworked OSGi support of Smack (SMACK-343)

Because of OSGi, no subproject of Smack (which is the same as a OSGi
bundle) must export a package that is already exported by another
subproject.

Therefore it was necessary to move the TCP and BOSH code into their own
packages: org.jivesoftware.smack.(tcp|bosh).

OSGi classloader restrictions also made it necessary to create a
Declarative Service for smack-extensions, smack-experimental and
smack-lagacy (i.e. smack subprojects which should be initialized), in
order to initialize them accordingly, as smack-core is, when used in a
OSGi environment, unable to load and initialize classes from other smack
bundles. OSGi's "Service Component Runtime" (SCR) will now take care of
running the initialization code of the particular Smack bundle by
activating its Declarative Service.

That is also the reason why most initialization related method now have an
additional classloader argument.

Note that due the refactoring, some ugly changes in XMPPTCPConnection
and its PacketReader and PacketWriter where necessary.