Add lint job to build workflow (#363)

* Add lint job to build workflow

* Add prettier-plugin-import-sort

* Install prettier plugins before linting

* Use lint script from package.json

* Move linters to separate workflow

* Remove Python and Shell linters

* Remove popd

* Test that prettier properly fails the lint job

.github/workflows/lint.yml

@@ -0,0 +1,17 @@
+name: Lint
+
+on:
+  push:
+
+jobs:
+  lint:
+    name: Run linters
+    runs-on: ubuntu-20.04
+
+    steps:
+      - uses: actions/checkout@v2 # Check out the repository first.
+      - name: Run prettier (JavaScript & TypeScript)
+        run: |
+          pushd frontend
+          npm install
+          npm run lint