Cannot run model contained in a project with white spaces in the name

The sequential java engine crashes when trying to initialize the context if the model to execute is contained in a project with a white space in the name.

Step to reproduce the issue:
* get the K3FSM language in the first language workbench
* in the modeling workbench, get the example model, create a new project with a white space( "test test" for example), copy the model in it, close the origin project, create some Sirius representation, create a launch conf and start the execution

It will fail with an exception similar to:

```
org.eclipse.gemoc.executionframework.engine.commons.EngineContextException: Cannot initialize the execution context, see inner exception.
at org.eclipse.gemoc.executionframework.engine.commons.AbstractModelExecutionContext.(AbstractModelExecutionContext.java:62)
at org.eclipse.gemoc.execution.sequential.javaengine.SequentialModelExecutionContext.(SequentialModelExecutionContext.java:27)
at org.eclipse.gemoc.execution.sequential.javaengine.ui.launcher.Launcher.createExecutionEngine(Launcher.java:38)
at org.eclipse.gemoc.execution.sequential.javaengine.ui.launcher.Launcher.createExecutionEngine(Launcher.java:1)
at org.eclipse.gemoc.executionframework.engine.ui.launcher.AbstractSequentialGemocLauncher.launch(AbstractSequentialGemocLauncher.java:108)
at org.eclipse.debug.internal.core.LaunchConfiguration.launch(LaunchConfiguration.java:859)
at org.eclipse.debug.internal.core.LaunchConfiguration.launch(LaunchConfiguration.java:717)
at org.eclipse.debug.internal.ui.DebugUIPlugin.buildAndLaunch(DebugUIPlugin.java:1039)
at org.eclipse.debug.internal.ui.DebugUIPlugin$8.run(DebugUIPlugin.java:1256)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:60)
Caused by: org.eclipse.core.internal.resources.ResourceException: Resource '/test%20test' does not exist.
at org.eclipse.core.internal.resources.Resource.checkExists(Resource.java:327)
at org.eclipse.core.internal.resources.Resource.checkAccessible(Resource.java:201)
at org.eclipse.core.internal.resources.Project.checkAccessible(Project.java:142)
at org.eclipse.core.internal.resources.Folder.assertCreateRequirements(Folder.java:33)
at org.eclipse.core.internal.resources.Folder.create(Folder.java:93)
at org.eclipse.core.internal.resources.Folder.create(Folder.java:121)
at org.eclipse.gemoc.executionframework.engine.core.ExecutionWorkspace.createFolder(ExecutionWorkspace.java:84)
at org.eclipse.gemoc.executionframework.engine.core.ExecutionWorkspace.createExecutionFolders(ExecutionWorkspace.java:76)
at org.eclipse.gemoc.executionframework.engine.core.ExecutionWorkspace.createExecutionContext(ExecutionWorkspace.java:72)
at org.eclipse.gemoc.executionframework.engine.core.ExecutionWorkspace.(ExecutionWorkspace.java:37)
at org.eclipse.gemoc.executionframework.engine.commons.AbstractModelExecutionContext.(AbstractModelExecutionContext.java:49)
... 9 more
```

apparently, the URI uses "%20" for white space and this not correctly handled when converting to path