Various tweaks and fixes for using EXWM

* .Xresources.d/xterm: Allow send events, needed for EXWM's simulation
keys to work.
* .emacs.d/init.el: Check additionally that we're in a graphical
environment, though not in another window manager or desktop
environment, before running EXWM.  Also, use the EXWM-provided
function for switching buffers that also works for EXWM windows,
including windows in other workspaces or those that are floating.
* .emacs.d/lisp/bandali-exwm.el: Tweak and add to global and
simulation keys for more convenience.
* .gnupg/gpg-agent.conf: It seems we need to explicitly set a
pinentry-program, otherwise GPG will pick the tty or ncurses one even
when we're not in a tty or terminal, which will not work and cause
problems when using EXWM.