Add support for the new handshake and for streaming compression.

A new handshake format was introduced in Quassel 0.10.  This patch
adds support for that.  Streaming compression support, which is
made possible by the new handshake, is also introduced.  All
legacy functionality (connecting to pre-0.10 cores and to cores
that don't support streaming compression and/or SSL) is preserved.
Additionally, support for enabling/disabling SSL in the core
creation dialog was removed because there is no reason not to use
SSL if it is available.

One unrelated change was made to preferences.xml because Android
Studio wouldn't stop yelling at me until I did.