Refactor development flow

[soanvig]

• [x] Closes #133
• [x] Closes #124
• [x] Streamline local manual testing (webpage and mm-jsr)
• [x] Cleanup where everything builds
• [x] use yarn v2
• [x] Describe development flow in contributing guide
• [x] Uncomment branch filter in webpage workflow

[soanvig]

Check for size limit doesn't pass because master use different version of yarn, but that's OK