Package csrfguard.js in JAR and look there by default

Adds csrfguard.js to the list of resources built into the JAR and modifies JavaScriptServlet to look in the JAR by default. Other small changes to support development and testing:

* Example JavaScriptServlet configuration uses the default value for `source-file`
* `csrfguard-test` project's `pom.xml` updated to use the same version as the main project (`3.1.0-SNAPSHOT`), which was necessary to get it to pick up the right code from the other project
* The `csrfguard-test` project's Tomcat now listens on port 8000 rather than port 80 as on many systems binding to port 80 requires elevated privileges
* Added GPG requirement to build notes

One additional note: I couldn't find an editor that would sanely deal with the tabs in the source files, so I gave up and used spaces in the diffs. I know this may be a huge source of frustration, so please feel free to reformat for consistency using the right tool. To support future collaboration, though, I'd recommend adopting a policy of disallowing tabs in non-binary source files. Replacing tabs with four spaces is a common style for Java source. A style validator such as [checkstyle](http://checkstyle.sourceforge.net/) with a very simple configuration might help enforce this.