This uses go-bindata/go-bindata to bundle the template in the binary.

I also realized that the handler test was now broken because we were
checking the exact contents of the index page in the test. This change
fixes that too.

This commit modernizes the repository organization a bit.

In short, this,

- Upgrades to Go 1.11.
- Uses Go modules instead of Glide.
- Drops errcheck, which we rarely use in our codebase internally.
- Uses `./...` to run build, tests, etc. since that does not have to
  account for vendor anymore.
- Drops `-installsuffix cgo` from the production build. This was a
  workaround for pre-1.10 versions of Go. See
  https://github.com/golang/go/issues/9344#issuecomment-69944514.
- Uses a tools.go as recommended in [go-modules-by-example/tools][1] to
  pin to tool dependencies.
- Uses `go run` instead of `go install`ing tools globally.

[1]: https://github.com/go-modules-by-example/index/tree/master/010_tools

Tested locally with `make docker-launch`.

The dependencies for this repository haven't been updated in a while.
This commit updates its dependencies, updating the import path for
staticcheck in the process.