submodule for geoserver war creation using war overlay with additional jetty configuration for execution. 

Creates an additional submodule that generates a geoserver war with the geomesa extension (and it's dependencies) injected.

The geoserver versions 2.4 or older the geoserver war will need to be added to a maven repository (local or remote). One can accomplish this with the following instructions from the command line:
```
mkdir geoserver-2.3.5-war
cd geoserver-2.3.5-war/
wget http://downloads.sourceforge.net/project/geoserver/GeoServer/2.3.5/geoserver-2.3.5-war.zip
unzip geoserver-2.3.5-war.zip
jar xf geoserver.war META-INF
mvn install:install-file -Dfile=geoserver.war -DpomFile=META-INF/maven/org.geoserver.web/web-app/pom.xml -DgroupId=org.geoserver.web -DartifactId=web-app -Dversion=2.3.5 -Dpackaging=war
```

The geoserver war can then be built with:
```
cd geomesa-geoserver
mvn clean install
```

The war built by this submodule can then be launched with
```
mvn jetty:run-war
```

The port for the jetty execution can be changed my passing with the property `jetty.port`, e.g.:
 ```
mvn jetty:run-war -Djetty.port=8081
```

The submodule is not added to the parent `pom.xml` since the geoserver war is not yet widely available in maven repositories.