Add fallback to WM_NAME

[kitt-cat]

wmctrl only reads _NET_WM_NAME, however some applications (e.g. steam) do not set it and only set WM_NAME.

When _NET_WM_NAME is missing, wmctrl gives the name as N/A; in such a case there is a chance we can still get the right name from WM_NAME.

Fixes https://github.com/mkropat/jumpapp/issues/75