MB-8989 display warmup progress

- on bucket detail page
- on node detail page

information currently displayed:
1. warming status
2. number of keys warmed/total number of keys
   for 'loading keys' status
3. number of values warmed/total number of values
   for 'loading data' status

estimated time of warming is not available in ep_engine stats
as of right now. the separate ticket will be created for adding
the estimated time

Change-Id: Iee8871871725329ad9e189d0de1d0e0db8672430
[alk@tut.by: rebased]
[alk@tut.by: fixed warmup_stats typespec]
Reviewed-on: http://review.couchbase.org/31754
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>