Select a class name when opening a builder

[BECATRUE]

This closes #223.

I updated the followings:

• thread.py: ExperimentInfoThread to emit with all experiments class info of the given experiment path.
• apps/explorer.py: After the experiment info is fetched, show a QInputDialog.
• apps/builder.py: Similar to explorer.py.
• Unittests for explorer and builder app.

Now, once we clicked the open button in explorer app, a QInputDialog appears.