Add support for building pogo with java17
To do so xtext must be updated to the latest version (>2.26.0.M2) and so we need a major refactoring to support this version as well.
So in the same move a bunch of files were moved to get rid of the fr.esrf.tango namespace and have a more classical maven project architecture.
The name of the xmi schema was changed from the fr.esrf.tango namespace as well. Note that this will cause xmi generated with this version not to be compatible with older versions.