Adds a ProgressBar class

[r-akemii]

In this PR we add a ProgressBar class in QAequilibraE.

Notes, brainstorming and so on

• Change dialog name in UI according to procedure
• Update labels and bar progress as necessary
• Remove label_2 and pbar_2 if not necessary and resize window -> this is sth we need to pair with the AequilibraE development because not all progress bars has two levels
• ProgressBar should open/close automatically when the process starts/finishes -> are we replacing all progress bars in QAequilibraE with this class?
• One issue with QAequlibraE's progress bars that has crossed my mind is setting a maximum value to account the progress -> we can set both minimum and maximum steps to 0 and the bar shows a busy indicator instead of a percentage (see: https://doc.qt.io/qt-6/qprogressbar.html#details).
• Can QGIS crash with the number of signals received by the progress bar? - Is it sth we should keep an eye on?
• What do we do when we have finished_threaded_procedure?

Existing progress bars

1. Desire lines
2. Simple TAG
3. Load dataset
4. Load matrix
5. Add connectors
6. Network preparation
7. Impedance matrix
8. Traffic assignment (from AequilibraE) (check on QGIS)
9. Add zones
10. Create project from OSM
11. GTFS importer (from AequilibraE)

TO-DO

• Tests
• Docs