Migrate from esc to packr for static files

generate/static.go

server/a_server-packr.go

server/static/generate.go

server/static/static.go

server/web.go

vendor/github.com/gobuffalo/packr/LICENSE.txt

vendor/github.com/gobuffalo/packr/README.md

vendor/github.com/gobuffalo/packr/box.go

vendor/github.com/gobuffalo/packr/builder/box.go

vendor/github.com/gobuffalo/packr/builder/builder.go

vendor/github.com/gobuffalo/packr/builder/clean.go

vendor/github.com/gobuffalo/packr/builder/file.go

vendor/github.com/gobuffalo/packr/builder/pkg.go

vendor/github.com/gobuffalo/packr/builder/tmpl.go

vendor/github.com/gobuffalo/packr/builder/visitor.go

vendor/github.com/gobuffalo/packr/env.go

vendor/github.com/gobuffalo/packr/file.go

vendor/github.com/gobuffalo/packr/file_info.go

vendor/github.com/gobuffalo/packr/go.mod

vendor/github.com/gobuffalo/packr/packr.go