Added support for SQLite.

This means some breaking changes since we've dumped the database connector.
Alice is no longer aware of more than one database. There is no fallback. If
fallback is required in a setup, then this is something that must be done outside
of Alice, ie. using database connection proxies or failover systems. Also this
change means that Alice now defaults to a local SQLite database. It should be as
easy as possible to get her up and running, and a local SQLite database is in
every possible way easier to get going than a PostgreSQL (or other proper RDBMS).
Minor reformatting.
Renamed <not> element object and attached messages to exceptions.
Type representing <day-of-week> elements.
Type representing <day-of-month> elements.
Package with calendar data for Denmark (DK).
Saturdays and Sundays are not banking days in Denmark.
Including holidays relative to Easter.  (Consider if the Easter calculation should be made public or moved to Calendars.Gregorian.)
Type representing <month> elements.
Type representing <DK-bankdag> elements.
Official holidays for Denmark matches those listed on <http://da.wikipedia.org/wiki/Danske_helligdage#De_danske_helligdage>.
Type representing <DK-helligdag> elements.
Type representing <DK-første-bankdag-i-måneden> elements.
Type representing <DK-ugenummer> elements.
Complete information on Danish 'bankdage'.
Dropped country specific calendar data in favour of a look-up based solution.  (DTD and example dial-plan change.)
Minor updates to INSTALL and README
Dropped country specific calendar data in favour of a look-up based solution.  (Ada types.)
Minor reformatting and additions.
Added the customers.db and test.db SQLite databases.