Build all GeCoS projects from sources

The bash script build.sh can be used to create a composite GeCoS project structure with all the bundles, features and tests from all the submodules (GeCoS projects) as well a composite update site.

• It creates the file structure in the directory build, which is first cleaned if it already exists.
• It links all the bundles, features and tests from all the submodules to corresponding locations in build.
• It creates all the necessary pom.xml files
• It invokes mvn from build. The command line arguments, if specified, are used as mvn options. Otherwise, the script exits after constructing the composite project structure.

WARNING: this script is only tested on ubuntu1604.