Explicitly set locale to en-US for executing tests.

There are test cases in RendererUtilsTest that expect date formatting to
result in particular strings, even though these strings are dependent on
the current system locale. (Very common mistake among Java programmers,
to assume anything about the system locale.) This addition to pom.xml
therefore sets the locale to en-US explicitly when executing tests.
Add exec.mainClass property so that "mvn exec:java" will start the app.
Merge remote-tracking branch 'remotes/local/fix-existing-code' into fix-existing-code