MB-8009: couchbase logo update on UI

Change-Id: I2358dc38ebfc9800185928bb3c867a16c88b9b47
Reviewed-on: http://review.couchbase.org/26117
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>