fix config setting and add file uploads

[CorentinDeBoisset]

Description

The method to update configuration keys forced a type cast into Boolean for any value, including string keys. This PR removes this cast.

I also added a file-upload feature, and edited tests so that they did not depend on pwpush.com to work (or even be logged in).

Related Issue

#655

Type of Change

• 📚 Examples / docs / tutorials / dependencies update
• 🔧 Bug fix (non-breaking change which fixes an issue)
• 🥂 Improvement (non-breaking change which improves an existing feature)
• 🚀 New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 🔐 Security fix

Checklist

• I've read the CODE_OF_CONDUCT.md document.
• I've read the CONTRIBUTING.md guide.
• I've updated the code style using make codestyle.
• I've written tests for all new methods and classes that I created.
• I've written the docstring in Google format for all the methods and classes that I used.

[pglombardo]

Python package 0.10.0 with this fix is out: https://pypi.org/project/pwpush/