Patch to easily run continuum jetty with postgres

The attached patch will allow running jetty against a postgres database.

As configured, postgres must be localhost, and have two databases named continuum and users which are accessible by user continuum with password continuum.

It uses a profile and a property to point to a different jetty-env.xml file with that configuration in it.

It can be launched with the command

mvn -Ppostgres81 jetty:run

from within the continuum-webapp directory.

I think (but haven't tested it) that the patch also allows pointing to any arbitrary jetty-env.xml file by using a launch similar to:

mvn -Djetty.env.xml=/path/to/jetty-env.xml jetty:run