New C4 Modules

New C4 Modules

* C4::Category
  - patron categories as objects
  - an all() method to return all the categories as a list
* C4::ItemType
  - itemtypes as objects
  - an all() method to return all the item types as a list
* C4::ItemCirculationAlertPreference
  - wrapper around the item_circulation_alert_preference table
  - create() and delete() methods for easy manipulation of the preferences
  - I regret giving it such a long name.
  - The item_type column should've been named itemtype to make it
    more similar to pre-existing tables.  Oh well.

(C4::Category and C4::ItemType were made so that I wouldn't have to
write SQL inside my CGI scripts.
Their main purpose is to provide an easy way to get a list of
patron categories and item types.
Do not be fooled by the amount of POD.
There's actually very little code in these modules.)

Signed-off-by: Daniel Sweeney <daniel.sweeney@liblime.com>
Signed-off-by: Galen Charlton <galen.charlton@liblime.com>
Signed-off-by: Henri-Damien LAURENT <henridamien.laurent@biblibre.com>