update of copyright info
Fix race condition on shutdown

This commit fixes primarily a race condition that occurs when xinit(1) shuts
down: by not acting properly fluxbox gets caught in an infinite loop. It
caused bug #1100.

xinit(1) sends a SIGHUP signal to all processes. fluxbox tries to shutdown
itself properly by shutting down workspaces and screens. While doing that, the
Xserver might be gone already. Additionally, fluxbox used to restart() itself
on SIGHUP, which is clearly not the right thing to do when xinit(1) is about
to end the session.

So, fluxbox does this:

* handling SIGHUP now shuts down fluxbox without clearing workspaces and
  screens.

* A 2 second alarm() is triggered in Fluxbox::shutdown() as a last resort

* XSetIOErrorHandler() is used to recognize the disconnect from the xserver.

* SIGUSR1 is for restarting fluxbox, SIGUSR2 for reloading the config

* FbTk/SignalHandler.cc/hh is gone; this unused abstraction served currently
  no real purpose. Signal handling is now done in main.cc

* Unrelated to the issue itself src/main.cc was trimmed down quite a bit and
  the code (responsible for handling the command line interface) was moved to
  src/cli*