Backend for x-by-y widget with 'group by'

New 'group by' parameters available.  Columns in metadata now
include a 'canGroup' property indicating they are available to use
in a group clause.  Specify each as its own querystring parameter,
e.g. /data/x-by-y?group=Currency&group=Day

You can select only successful donations with
$filter=Action eq 'process' and Status eq '1'
or only failed donationis wtih
$filter=Action ne 'process' or Status ne '1'

Change-Id: I8f7a8c344b7aba4a9f39d97a86b9d9a46c42c413
Merge "Backend for x-by-y widget with 'group by'"