Rename filenames in the assets package to align with incoming i18n one:
- data.go is what is generated for embeeded assets
- dev.go is the helper to load assets on disk, live. "dev" tag
- embedded.go is the helper to load embedded assets (enables as well
running the generator for go generate without tags)
- external.go is the helper to load assets installed on disk
- gen_data.go generates data.go
- install_data.go installs data on disk.