Compatibility fixes for download.sh

[alxivnov]

1. Added curl for macOS compatibility. macOS doesn't have wget, but has curl by default.
2. Fixed conflict with existing LICENSE file. Since repo already contains LICENSE file and wget is used with --continue, download of the license is trying to resume from the byte offset further then actual license on the server.
3. Moved leading zero from seq -f to url for Alpine/BusyBox compatibility. BusyBox-based Linux distros don't support -f option for seq, so leading zero is added directly to model's filename consolidated.0${s}.pth.

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