Online screenshot diff/generation using CircleCI (#1187)

* Add CircleCI config for online screenshot verification/generation

* Remove `Checkout unicode fonts` step

Unicode-fonts are now a submodule, which is checked out in `Checkout submodule` step.

* Always generate new screenshots

.circleci/config.yml

@@ -0,0 +1,57 @@
+defaults: &defaults
+  steps:
+    - checkout
+    - run:
+        name: Checkout submodule
+        command: |
+            git submodule sync
+            git submodule update --init --recursive
+
+    - restore_cache:
+        keys:
+          - npm-deps-{{ checksum "package.json" }}
+          - npm-deps-
+    - run:
+        name: Install npm dependencies
+        command: npm install
+    - save_cache:
+        key: npm-deps-{{ checksum "package.json" }}
+        paths:
+          - node_modules
+
+    - run:
+        name: Verify screenshots and generate diff
+        command: node dockers/Screenshotter/screenshotter.js --seleniumIP localhost -b $CIRCLE_JOB --verify --diff
+    - run:
+        name: Generate new screenshots
+        when: always
+        command: |
+            rm -rf test/screenshotter/images/*
+            node dockers/Screenshotter/screenshotter.js --seleniumIP localhost -b $CIRCLE_JOB
+
+    - store_artifacts:
+        path: test/screenshotter/images
+        destination: image
+    - store_artifacts:
+        path: test/screenshotter/diff
+        destination: diff
+
+version: 2
+jobs:
+  firefox:
+    docker:
+      - image: circleci/node:6
+      - image: selenium/standalone-firefox:2.48.2
+    <<: *defaults
+  chrome:
+    docker:
+      - image: circleci/node:6
+      - image: selenium/standalone-chrome:2.48.2
+    <<: *defaults
+
+workflows:
+  version: 2
+  screenshotter:
+    jobs:
+      - firefox
+      - chrome

dockers/Screenshotter/README.md

@@ -48,6 +48,11 @@ fashion are well suited for visual inspection, but for exact binary
 comparisons it would be neccessary to carefully set up the environment
 to match the one used by the Docker approach.
 
+You can also verify and generate screenshots online using a CI(continuous
+integration) service. Fork the project, enable [CircleCI](https://circleci.com/) on your repository,
+and push your changes. Diffs and generated screenshots are available at
+build artifacts.
+
 ## Choosing the list of test cases
 
 Both `screenshotter.js` and `screenshotter.sh` will accept