Added some missing JRE methods and implemented a very first maven client-side compiler plugin

I compiled my GameEngine using Dragome and there is a simple demo available here:

http://www.mirkosertic.de/games/dukeplatform_dragome/

To make this run, i had to add some missing methods to the JRE and also write a Maven plugin to compile the engine to JavaScript. The result can now be deployed to a simple WebServer without Java support on server side at all!

The maven plugin can be used as follows:

```xml
            <plugin>
                <groupId>com.dragome</groupId>
                <artifactId>dragome-maven-plugin</artifactId>
                <executions>
                    <execution>
                        <phase>prepare-package</phase>
                        <goals>
                            <goal>compileclient</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <destinationDirectory>${project.build.directory}/${project.build.finalName}</destinationDirectory>
                    <forceRebuild>true</forceRebuild>
                    <removeCache>true</removeCache>
                </configuration>
                <dependencies>
                    <!--  Your Project dependencies go here 
                    <dependency>
                        <groupId>de.mirkosertic</groupId>
                        <artifactId>gameengine-dragomerenderer</artifactId>
                        <version>${project.version}</version>
                    </dependency> -->
                </dependencies>
            </plugin>
```