Bug 7955: Statistics tab for Patron checkouts

Bug 7955: Statistics tab for Patron checkouts

This patch adds a new 'statistics' tab in the Patron module.
For a borrower, this tab contains a table with:
- number of checkout for today
- number of checkin for today
- "precedent state", the number of checkouts the patron had yesterday on
  its library card
- "actual state", the number of checkouts on the borrower card at the current date

A new syspref (StatisticsFields) contains a list of fields (separated by
pipe (|) on which the table results is based. The default value is
location|itype|ccode

Signed-off-by: Mathilde Formery <mathilde.formery@ville-nimes.fr>