Allow Syn to be disabled on the Tomcat valve

[whikloj]

Allow people to easily disable the Syn Valve without having to remove the jar file and configuration.

[kstapelfeldt]

@whikloj do we need to add something to a readme to document this?

We think this has to do with being able to turn off how Fedora does authentication so that you can switch back and forth between Islandora authentication and Fedora's web interface. This is a config.xml thing that can be updated. It's a dev tool.