Don't build UI plug-ins when just building the probe.
Don't build UI plugins when only building the probe.
Qt5::Widgets is required when building the UI.
Build this test only if Qt5::Widgets is available.
Add GAMMARAY_BUILD_UI option, alongside GAMMARAY_PROBE_ONLY_BUILD.

Their semantics were kinda mixed until now, but we need both:
- GAMMARAY_PROBE_ONLY_BUILD is for building another probe with a different
  ABI, while reusing an already built launcher and client.
- GAMMARAY_BUILD_UI is for disabling building the client and in-process UI
  plug-ins, for example when building for an embedded target.
GAMMARAY_BUILD_UI implies we have widgets.

So we can simplify these conditions to not check for widget availability
as well.
Port to GAMMARAY_BUILD_UI.
Only start the refresh timer after having processed the results.

On slow systems with long process lists we might call updateProcesses()
faster than it needs to finish otherwise.
wk2application requires Qt5Quick
Add missing license headers.
Enable usage of Q_DECL_OVERRIDE with Qt4.
Factor out server greeting code into its own method.
Make serverAddress() return an URL.

This is done in order to support different transport mechanisms.
Add abstraction for transport mechanisms on the server side.

So far only covering TCP/UDP, as before.
Change the broadcast message format to contain server URLs.

Removes the assumption we are connecting via TCP.
Use the server URL rather than reading from probe settings directly.
Send the server address as URL.
Send the entire server address back to the launcher, not just the port.
Add support for using local sockets as transport.

That's going to be needed on Android when not having the network access
permission.
Support URLs as user input for --connect and --listen.