Ship assets in compiled binary.

With that change, we can deploy the prometheus binary without the need to ship assets/templates separately.

- utility/embed-static.sh, get called in Makefile to create go map from files (gzip, hex byte array)
- web/blob/blob.go implements http Handle for serving the files from the map
- web/status.go uses blog.GetFile() to get the template file

The assets are gzipped and decompressed on demand.