Add GitHub actions CI scripts

.github/workflows/ci/linux.yml

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+name: Build Linux Client
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Clone source code
+        uses: actions/checkout@v1
+      - name: Use Node.js
+        uses: actions/setup-node@v1
+        with:
+          node-version: 10.x
+      - name: Install dependencies and build
+        run: |
+          npm install
+          npm run build --if-present
+          npm run build-desktop-linux

.github/workflows/ci/mac.yml

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+name: Build macOS Client
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: macos-latest
+
+    steps:
+      - name: Clone source code
+        uses: actions/checkout@v1
+      - name: Use Node.js
+        uses: actions/setup-node@v1
+        with:
+          node-version: 10.x
+      - name: Install dependencies and build
+        run: |
+          npm install
+          npm run build --if-present
+          npm run build-desktop-darwin-nosign

.github/workflows/ci/standard.yml

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+name: Node CI
+
+on: [push]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [8.x, 10.x, 12.x]
+
+    steps:
+      - name: Clone source code
+        uses: actions/checkout@v1
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v1
+        with:
+          node-version: ${{ matrix.node-version }}
+      - name: Install dependencies and build
+        run: |
+          npm install
+          npm run build --if-present
+        env:
+          CI: true

.github/workflows/ci/win.yml

@@ -0,0 +1,21 @@
+name: Build Windows Client
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: windows-latest
+
+    steps:
+      - name: Clone source code
+        uses: actions/checkout@v1
+      - name: Use Node.js
+        uses: actions/setup-node@v1
+        with:
+          node-version: 10.x
+      - name: Install dependencies and build
+        run: |
+          npm install
+          npm run build --if-present
+          npm run build-desktop-win