5ff978a52b
input-method-v1 protocol provides two surface type for the input panel, `toplevel` and `overlay`. But there is no example for the later one. This change enables to set weston-keyboard as overlay panel by the environment variable `WESTON_KEYBOARD_SURFACE_TYPE=overlay` to demonstrate this feature. In Addition, add weston.ini option `overlay-keyboard` to set it. Signed-off-by: Takuro Ashie <ashie@clear-code.com>