Update devicefesawidget

This MR contains the following changes

1 - Separated the model from the View/Controller logic in DevicesFesaWidget

2 - Refactored all classes using private methods to init the UI + docstrings + type hints

3 - Added new search parameters to the device search classes_to_search, fecs_to_keep, acc=acc, devices_to_keep (useful for comparing config files with ccda), devices_to_remove

4 - Added the option to pass a custom QPushButton widget to serve as the device button in DeviceClassPanelWidget

5 - Implemented the tree view widget

6 - Improved/ extended the examples

• example1 "Basic Configuration using class tabs and grouping by FEC"
• example2 "Non-Grouped BOBRs from LHC"
• example3 "Using devices_to_hide and a title"
• example4 "Using devices_to_filter"
• example5 "Using custom Device Widget"
• example6 "Tree View"