backend-x11: Re-upload keymap when new keyboard devices are added

The X server applies a default keymap to hotplugged keyboard
devices. To enforce our current settings we must re-upload the keymap
when a new keyboard shows up.

Note that setting the VCK keymap causes the server to propagate it
to all slave keyboard devices.

https://bugzilla.gnome.org/show_bug.cgi?id=737673
backend-native: Handle keyboard repeat settings

We need to tell clutter's evdev backend about the desktop's key repeat
settings so that our own key bindings event processing and
gnome-shell's chrome widgets get their fake key events for continuous
key press as they expect.

Note that the wayland frontend filters out these events and thus
wayland clients do not see them as specced.

https://bugzilla.gnome.org/show_bug.cgi?id=728055