CreateNewGemocSequentialLanguageProject should not directy inherit from NewMelangeProjectWizard

[CreateNewGemocSequentialLanguageProject](https://github.com/eclipse/gemoc-studio-modeldebugging/blob/master/java_execution/java_xdsml/plugins/org.eclipse.gemoc.execution.sequential.javaxdsml.ide.ui/src/org/eclipse/gemoc/execution/sequential/javaxdsml/ide/ui/wizards/CreateNewGemocSequentialLanguageProject.java) currently inherits from NewMelangeProjectWizard

This was making sense when there were only melange as input, but now we are considering other project structure (such as DSL file + k3 only, xmof, ...)
so now it would be better to have a new GEMOC project that would be "technology" agnostic, then have templates (contributed as extension like current ones) that would finalize the project with appropriate content and natures.

Note: in case of reuse between related templates, they can inherit of a common base or use a composition approach