Add gradle to project

Add gradle to the project to have an unified build-process on all
platforms.
Add gradlew description in README
Merge pull request #1 from rotespferd/master

Add gradle to project.
Add support for IDEs to gradle file
Add files for eclipse and idea to .gitignore file
Add creation of projects to README
Merge pull request #2 from rotespferd/master

Add support for IDEs in gradle.