MB-10086: implemented ui for clusterwide logs collection

This is based on initial work by Pavel Blagodov:
http://review.couchbase.org/#/c/34474/

Most of the work is Pavel's. All bugs are mine.

Change-Id: I085810cdfcaedb9c19173dd797d30c18f50d4554
Reviewed-on: http://review.couchbase.org/37825
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>