better version management in maven POMs

[dumoulin]

For now, version of the projects in trunk are tagged to 0.3. It should be tagged as 0.3_SNAPSHOT.

Then tagging should be done using the maven release plugin. But we have to investigate how it will manage multi-modules project. In particular, if we run this plugin on the super POM, how manage module that inherits from this one, but are not included as composition (in <modules> section).