MB-9979: implemented basic UI for delta recovery

This uses html/css markup work by Pavel Blagodov.

Change-Id: I1ffa1ec2cc0536a17120a74dabecb17c038bf9dc
Reviewed-on: http://review.couchbase.org/34252
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>