Visiannot

* Add URL to Digi-NewB project in "about" popup window

* New synchronization scheme

* The user chooses a temporal range duration for splitting the long recording into several "files"
* The videos may not be synchronized, it is not the reference for synchronization anymore

* Feature "truncated temporal range duration" removed
* New layout mode for screen with portrait orientation
* Fake events annotation "DURATION" removed
* Suffix "-datetime" removed from events annotation paths

* Bugfix in setup.py for "pip install" (opencv version must be below 4)
* Bugfix for updating ticks of progress widget when changing file with custom temporal range widget
* Bugfix for events annotation

* Optimization of signal data loading in asynchronous long recording
* Modification of signal configuration
* New API compliant with PEP8
* Possibility to select a column value in 2D data for signal
* Option for allowing events annotation overlap
* Frame format of events annotation removed
* Timestamp format of events annotation with standard microseconds instead of milliseconds

- In documentation, add link to repository with example dataset
- Bug fix for conversion of string to datetime => resolve bug of events annotations display
- Bug fix in the constructor of ConfigurationWindow when passing a configuration file path
- Ability to pass a configuration file path to ViSiAnnoTLongRecFromGUI
- Add argument to __main__.py in order to pass a configuration file path

- Add __main__.py in the package so that ViSiAnnoT can be launched with a command line after installation (python3 -m visiannot)
- Bug fixes for documentation building in ReadTheDocs