* exwm-core.el: New buffer-local variable exwm--mwm-hints.
* exwm-manage.el: New variable exwm--atom-_MOTIF_WM_HINTS for holding the
value of _MOTIF_WM_HINTS atom; new function exwm--update-mwm-hints for
updating the _MOTIF_WM_HINTS property of an X window.
* exwm-manage.el (exwm-manage--init): Intern the _MOTIF_WM_HINTS atom.
* exwm-manage.el (exwm-manage--manage-window): Avoid managing windows
without decoration (implied by _MOTIF_WM_HINTS).
* exwm-core.el: new buffer-local variable exwm--floating-mode-line-format for
saving mode-line-format when mode-line is hidden
* exwm-floating.el (exwm-floating--fit-frame-to-window)
(exwm-floating-hide-mode-line, exwm-floating-show-mode-line): new functions
for resizing frames, hiding/showing mode-line respectively;
(exwm-floating--set-floating): use exwm-floating--fit-frame-to-window to
resize frames