add `wfutils.el` for frame/window related fuctions

Most of the codes in `wfutils.el` are from `init/window-frame.el`.

I decided to organize the common code which other users can
use as a separated file, so that `init/window-frame.el`
contains customized code only.
add file comment to `ffap-java.el`
Merge remote-tracking branch 'origin/master'