The issue was that we never got a tile when the signals were
launched (this could have caused other issues as well).

The former was broken in a previous commit, the latter is now properly
introduced (as shaded windows still report the same geometry, we handle
them as we do fullscreen windows - not).

It is _strongly_ recommended for now to use FocusUnderMouse with this,
as it's otherwise almost impossible to tell which window is focussed.

Should also fix e.g. Firefox resizing.

This needs a couple of workarounds:

- Qt won't convert a QStringList to an Array, instead giving an utterly
  useless QVariant(QStringList) (without any methods and presumably only
  containing the pointer)

- The config group _needs_ to be empty, else it's not accessible from
  the javascript side

Always set tiling_floating.

(Also removes superfluous keepBelow setting)

Fullscreen windows should be above _everything_, so keepBelow should be false.

Prevents .xsession-errors from getting big.

This is much cleaner than the hodgepodge we had before
and also means e.g. desktopswitching can be handled correctly.

It is now effectively a layout.

This requires a semantics change: addClient can now also deal with already managed clients.

This also fixes a bug with tiling because a method was missing.