Christmas dates for Leicester

Leicester - Changed the dates and time
Updated WarrenHill and Whatton xmas dates
xmas dates up to Guys Marsh on xls doc
Updated Prison Christmas dates
I've sorted unbookable dates and slot anomalies lexicographically within the yaml files,
and enforced the order within tests. I *think* this will make git merges easier on these
files easier.
Mailer spec for reference in canned responses
Reference number does not appear in non-canned response emails