feat(gateway): split off cache into separate package, rename package to 'gateway'

Dockerfile.gateway

@@ -1,7 +1,7 @@
 # twilight requires newer rustc than what is in alpine:latest
 FROM alpine:edge AS builder
 
-RUN apk add cargo
+RUN apk add cargo protobuf
 
 # Precache crates.io index
 RUN cargo search >/dev/null
@@ -9,6 +9,9 @@ RUN cargo search >/dev/null
 WORKDIR /build
 COPY proto/ /build/proto
 COPY gateway/ /build/gateway
+COPY myriad_rs/ /build/myriad_rs
+
+# todo: cache build of myriad_rs elsewhere
 
 RUN (cd gateway && cargo build --release)