Allow user to change WM_NAME
Allow user to change WM_NAME

The old way to change `_NET_WM_NAME` using EWMH didn't work and was
always setting a fixed name. Now it uses `xcb::change_property` to set
`NET_WM_NAME` which seems to work properly according to `xprop`.

There now also is another property on the `BarBuilder` called
`window_title` which allows the user to change it.

dogamak/xcbars