luci-base: ui: implement addTimeLimitedNotification

luci-base: ui: implement addTimeLimitedNotification

Introduce addTimeLimitedNotification which extends addNotification,
with the addition of the 'timeout' parameter.

timeout: a millisecond value after which the notification will disappear
automatically. If omitted, the notification will remain until it
receives the click event.

Improved implementation of 53e36e3293bee2ea2ce0fbc1250074c44cfe8335

Signed-off-by: Paul Donald <[email protected]>
(cherry picked from commit 0329854049facca13736e193b9e5fd4909d8e90e)