menuconfig: add gconfig/xconfig support (#1509)

* change "pmbootstrap kconfig_check" to "pmbootstrap kconfig check"
* change "pmbootstrap menuconfig" to "pmbootstrap kconfig edit [-x|-g]"
  (with legacy alias, because the first syntax was referenced to a lot)
* enable X11 interfaces: -x: xconfig, -g: gconfig
* new function to copy the xauthority file:
  pmb.chroot.other.copy_xauthority()
* remove menufconfig() function from the kernel template and all kernel
  aports ([skip ci] because it would rebuild all kernels and run out of
  time). Alpine has dropped this as well, and it wouldn't work with the
  new code anyway.

test/test_chroot_interactive_shell.py

@@ -39,7 +39,7 @@ def test_chroot_interactive_shell_user():
     pmb_src = os.path.realpath(os.path.join(os.path.dirname(__file__) + "/.."))
     os.chdir(pmb_src)
     ret = subprocess.check_output(["./pmbootstrap.py", "-q", "chroot",
-                                  "--user"], timeout=300, input="id -un",
+                                   "--user"], timeout=300, input="id -un",
                                   universal_newlines=True,
                                   stderr=subprocess.STDOUT)
     assert ret == "pmos\n"