Add capability to migrate to Gradle build

Here is an initial set of files to start the facilitation of a migration to Gradle. This is by no means ready yet, but by trying it out we should get a better idea of what is still needed.

## Files
* `gradle/`, `gradlew`. `gradlew.bat` - The ususal Gradle wrapper stuff
* `pom2gradle.gradle` - A gradle script to create a `build.gradle` file from the `pom.xml` file In this way we can easily test gradle builds after changes to the Maven POM were made
* `build.gradle` - The real build file as create by `pom2gradle.gradle`

## Building
`./gradlew build --info`

Currently Gradle builds will end up in `buildGradle` directory. 

## Comparing against Maven build
There is a special task that will compare the JAR created by Gradle with that of Maven. It will create a report in `buildGradle/reports`. To run the comparison do `./gradlew compareJars --info`



## To recreate build.gradle
`./gradlew -b pom2gradle.gradle`