Attach an AbstractPluginView objects directly into the AbstractPluginController class instance
Make view implementation-dependent of controller

Interface AbstractExporterView.getDialog() method
Add a missing super() in AbstractPluginView.__init__() for method resolution order.
Merge remote-tracking branch 'otetard-github/feature/wireshark-requirements'
Prevent Netzob from starting if the current workspace is not valid

Before this patch, it was possible to start Netzob without specifying
a valid workspace. To occur, the user had to provide an invalid and yet existing workspace
directory twice. The second time, the XSD validation error didn't stop the application
from starting.

To fix this issue, the condition which verifies if the workspace exists and
is valid has been replaced by a while loop.