executionframework.engine.commons.DslHelper should not refer to sequential engine

[dvojtise]

the class https://github.com/eclipse/gemoc-studio-modeldebugging/blob/master/framework/execution_framework/plugins/org.eclipse.gemoc.executionframework.engine/src/org/eclipse/gemoc/executionframework/engine/commons/DslHelper.java explicitly refers to the org.eclipse.gemoc.gemoc_language_workbench.sequential.xdsml extension point which is specific to sequential engine (and more precisely to the java engine as it is defined there)

As this class is part of common, it should not refer to any specific engine. (it is used for example in several launchers)

proposition:
use a specific generic extension point in order to reference dsl files in the system (related to eclipse-gemoc/gemoc-studio#90 and eclipse-gemoc/gemoc-studio#58 ) is would be associated to a base builder+nature (or engines may just extend this base builder)

[dvojtise]

(see also discussion in eclipse-gemoc/gemoc-studio-execution-moccml#20)

Currently, the strategy to get the list of dsl files was to duplicate extension points so each engine would be able to refine it and add new features. However this leads to difficulties to retrieve all these dsl since they are scattered into multiple extension points
Additionally, these EP have to duplicate java code (in some case the behavior is inherited)

I suggest introducing a generic extension point at the framework level which contains all the general informations required by all engines. then if a given engine requires additional information it can declare its own extension point for the engine specific information (for example in the case of the moccml engine)

[dvojtise]

this is quite a high priority since this is a prerequisite to other refactorings