Remove case-insensitive file conflicts

[aloisklink]

Currently, some of the d3 claims have filenames that conflict with each other on case-insensitive file systems (used on Windows), e.g.:

• manufacturers/Sonos/device.type.d3.yaml
• manufacturers/SONOS/device.type.d3.yaml

@aloisklink We can change the script d3_populate to make sure that we don't have folders with the same name but different case.
Originally posted by @mereacre in #17 (comment)

After fixing these, we can add the rule check-case-conflict to our pre-commit config so it hopefully shouldn't happen again.