Improve handling of sessions and folders

[DanicaSTFC]

Improve the class:

eqt/ui/MainWindowWithSessionManagement.py

Note:

some issues related to this:
#34
#143

The class class MainWindowWithSessionManagement is inheriting from MainWindowWithProgressDialogs. It looks like we want to detach them.

The goal is to be able to substitute a generic QMainWindow, e.g. such as the one in iDVC, with a new class where the session management is handled.