add translation test (#857)

Adds a translation test github action, that creates a messages.pot using jambo extract-translations
and then checks that every .po file matches messages.pot.
This is the same logic that the SDK's translation test uses.
Also adds an Italian translation that was missing, so that tests pass.
Previously, the translation for `vertical-full-page-map-alternative-verticals/alternativeverticals.hbs:47` was used 
for `vertical-full-page-map-alternative-verticals/alternativeverticals.hbs:5` instead of the actual line 5 translation,
causing the translation for line 47 to be doubled and the translation for line 5 to be missing.

J=SLAP-1378
TEST=auto

checked that the test will run on master and release branches

.github/workflows/translation-test.yml

@@ -0,0 +1,33 @@
+name: Translation Test
+
+on:
+  pull_request:
+    branches:
+      - master
+      - release/*
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [15.x]
+    steps:
+    - uses: actions/checkout@v2
+    - name: Use Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v1
+      with:
+        node-version: ${{ matrix.node-version }}
+    - run: npm ci
+    - name: 'extract translations'
+      run: npx jambo extract-translations --globs '*/**/*{.hbs,.js}' '!**/node_modules' $IGNORED_FOLDERS --output $OUTPUT_FILE
+      env:
+        IGNORED_FOLDERS: '!{commands,hbshelpers,patches,postupgrade,static,tests,test-site,translations}/**'
+        OUTPUT_FILE: 'translations/messages.pot'
+    - run: sudo apt-get install -qq gettext
+    - run: |
+        cd translations
+        for po_file in *.po
+          do msgcmp $po_file messages.pot
+        done