Updating .xsd schemas with version numbers

Created by: mlauster

Our xsd schemas defining our teaserXML files etc. have currently no version number. That makes it hard to update them and keep track of old versions. This topic came up with #253 (closed), as fixing a typo in the xsd schema breaks backward compatibility if do not support loading old files as well. This is only possible if we check with which xsd version a file has been created and have binding classes for all versions accordingly. To handle this, we propose:

• Every xsd schema gets a version number. As we hopefully don't need to change them that often, we can aggregate some files to one version number.
• We keep only the xsd schema of the current version.
• We create a new directory structure with one directory per version.
• We keep the binding classes for all versions in their corresponding directory.