v2.0.0-beta.3

Deployed to: https://python.microbit.org/v/beta

• Added WebUSB Partial Flashing (#217) (#222) (#224) (#225) (#227) (#228) (#229)
• Improved WebUSB error handling (#211)
• WebUSB buttons are always displayed (#226)
• Help page updated with the new features (#199)
• Added Polish translation and updated Spanish translation (#206) (#210) (#230)
• Language can now be set via URL (#212)
• Accessibility improvements (#215) (#219)
• General UI improvements (#213)