Add ability to easily capture log outputs in unit tests

public class RestrictParseLocationEventHandlerTest
{
...
    /**
     * Capture logs with WARN or higher severity to assert them.
     */
    @Rule public LogRule logRule = new LogRule() {{
        record(LogLevel.WARN);
        recordLoggingForType(RestrictParseLocationEventHandler.class);
    }};

    @Test
    public void includeEventWhenIllegalPath()
    {
...
        Assert.assertEquals(1, this.logRule.size());
        Assert.assertTrue(this.logRule.contains(
            "Direct access to template file [/WEB-INF/xwiki.cfg] refused. Possible break-in attempt!"));
    }
}