Use Rust for the front-end too (#374)

Rust can compile to WASM, so let's use it for front-end code as well.

To compile the front-end:

```
cargo install cargo-web
cargo web deploy -p plume-front
```

Dockerfile

@@ -13,7 +13,9 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 WORKDIR /app
 COPY Cargo.toml Cargo.lock ./
 RUN cargo install diesel_cli --no-default-features --features postgres --version '=1.3.0'
+RUN cargo install cargo-web
 COPY . .
+RUN cargo web deploy -p plume-front
 RUN cargo install --path ./ --force --no-default-features --features postgres
 RUN cargo install --path plume-cli --force --no-default-features --features postgres
 RUN cargo clean