support jetty with postgres

tested with postgres 9.1 under ubuntu 13.04.
it turns out that postgres does not support blob like h2 does.
there are two alternatives, bytea and oid.

the JPA @Lob annotation that works for h2 blobs will
also work with postgres oid, but not with postgres bytea.

the oid implementation is faster than bytea, being implemented
as files outside the tables space, but guaranteed cleanup on
delete may be problematic.  not tested.
http://relation.to/15492.lace
no jetty dependency

this was needed for starting the webapp from within
eclipse via MainRunner.java, but I'm only testing
with mvn jetty:run now.
correct postgres jdbc dependency

the jdbc driver should not be included in the war,
but provided by the container hosting the war,
in this case the jetty plugin.
correct servlet-api scope

this should be provided by the container,
so does not need to be included in the war