libinput.h/evdev.c: Add definitions for LIBINPUT_LED_COMPOSE and LIBINPUT_LED_KANA

Blinkenlights status of The Great Five(Num,Caps,Scroll,Compose,Kana):

• Base Linux support - hopefully it works there, it's at least exposed and controllable in /sys
• Linux Scroll Lock support - seems broken
• libinput which fixes this issue
• kwin

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Fixes #818 (closed)

This probably should have tests added in test/test-keyboard.c?
I am not sure how to write them.

~~Is there a reason to implement only the first five keys, or would it be a good idea to do the rest too?~~

#define LED_NUML		0x00
#define LED_CAPSL		0x01
#define LED_SCROLLL		0x02
#define LED_COMPOSE		0x03
#define LED_KANA		0x04
#define LED_SLEEP		0x05
#define LED_SUSPEND		0x06
#define LED_MUTE		0x07
#define LED_MISC		0x08
#define LED_MAIL		0x09
#define LED_CHARGING		0x0a
#define LED_MAX			0x0f
#define LED_CNT			(LED_MAX+1)

EDIT: No, it doesn't, 1-5 seems to be official HID spec