Add prettier configuration

[MAILPOET-4075]

.prettierignore

@@ -0,0 +1,25 @@
+*.hbs
+.mp_svn
+_generated
+_output
+composer.json
+composer.lock
+node_modules
+vendor
+vendor-prefixed
+/.mp_svn
+/dev/data
+/mailpoet/assets/dist
+/mailpoet/assets/js/lib
+/mailpoet/assets/js/src/newsletter_editor/behaviors/tinymce_icons.js
+/mailpoet/generated
+/mailpoet/lang
+/mailpoet/lib/Newsletter/Renderer/Template.html
+/mailpoet/lib-3rd-party
+/mailpoet/plugin_repository
+/mailpoet/temp
+/mailpoet/tests/javascript_newsletter_editor/testBundles
+/mailpoet/tests/plugins
+/mailpoet/views
+/mailpoet-premium
+/wordpress

.prettierrc

@@ -0,0 +1,5 @@
+{
+  "printWidth": 80,
+  "singleQuote": true,
+  "trailingComma": "all"
+}