Ship assets in compiled binary.

- utility/embed-static.sh, get called in Makefile to create go map from files
- 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.
Replace popd/pushd because travis' /bin/sh doesn't support it.
Use constants for blob bucket keys.
Detect mime type on runtime instead of hardcoding.