Allow getting binaries from remote location

[LLFourn]

Rather than uploading a binary yourself through a POST request we should allow getting a .wasm binary from a remote location e.g. github repository. When you submit this you should already know the hash of it so i'd say submiting it by doing PUT /binaries/<binary hash> which can accept a url to the binary. I imagine a typical HTTP form string will work well here. e.g. url=https://github.com/path-to-my-binary/my-binary.wasm or github=llfourn/my-carol-program with some canonical place for putting the wasm binary for your program.

Only do the url one for now I guess. Also open to other ideas.

Consider:

• change the resource to wasm or wasm-binaries