Tapered tool calculation, major bugfix, minor optimizations

This release uses the pathfinding algo from 1.1 but has some tweaks in the details:

• QR-codengrave version now mentioned in the G-code file
• qr_ prefix add in file save dialog
• Bugfix for tool selection in G-code that (at least on my machine) wouldn't have the tool change macro called
• Some corner case "throw exception" issues fixed
• Better and more unit tests

QR-codengrave V1.1

• Upgraded path algorithm for lower machining times
• Several bugfixes (see commit history)
• Fully backwards-compatible to V1.0

Initial release for Windows

Initial Release.
Features:

• Drawing preview
• Tool table and selection
• Persistence module working
• XY-0-offsets
• Engrave parameter selection
• G-code export working (*.tap)
• Unit tests for QR-code path generator and G-code generator

Future features to implement:

• Optimize Drawing algorithm for speed
• Optimize path generator algorithm for less Z movements
• Add integration tests for GUI