Plume front arm support (#402)

* Update plume-front build to use a shell script that adds the necessary dependencies on arm (x86 left untouched inside the script)

* Fix cleanup portion of plume-front.sh

* Break wasm dependencies for arm out so they are run before the main builds to improve layer caching on subsequent docker builds

* Fixup dockerfile so wasm-deps can run properly and with fewer assumptions

* Move new scripts to script/ folder

* Remove saving of path as it's not actually not necessary

* Add rust-toolchain to early copy so it pulls the right rust release (addresses #400)

script/plume-front.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+
+ARCH=`arch`
+
+if [ "$ARCH" == "aarch64" -o "$ARCH" == "armv7l" ] ; then
+    export PATH=/opt/local/llvm/bin:${PATH}
+    cd /app
+    RUSTFLAGS="-C linker=lld" cargo web deploy -p plume-front
+else
+    cargo web deploy -p plume-front
+fi