First pass PipelineGraph UI component

Add PipelineGraph UI component using elkjs and vx.
It does not currently support user interaction (zoom, pan, click, etc.)
but this will come in future PRs.

Add storybook stories to cover the two main components:
- Node: represents a node in the graph (Task or Step)
- PipelineGraph: collection of Nodes + Links

package.json

@@ -26,9 +26,12 @@
     "@formatjs/intl-pluralrules": "^1.2.1",
     "@tektoncd/dashboard-components": "file:./packages/components",
     "@tektoncd/dashboard-utils": "file:./packages/utils",
+    "@vx/network": "0.0.192",
     "carbon-components": "^10.6.1",
     "carbon-components-react": "^7.6.1",
     "core-js": "^3.0.1",
+    "d3-path": "^1.0.8",
+    "elkjs": "^0.5.1",
     "es6-promise": "^4.2.6",
     "history": "^4.9.0",
     "isomorphic-fetch": "^2.2.1",

packages/components/src/components/Graph/Graph.scss

@@ -0,0 +1,89 @@
+/*
+Copyright 2019 The Tekton Authors
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+    http://www.apache.org/licenses/LICENSE-2.0
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+$edge-color: #979797;
+
+.pipeline-graph {
+  #edge-arrow path {
+    fill: $edge-color;
+    stroke: $edge-color;
+  }
+
+  .vx-network-links path {
+    stroke: $edge-color;
+    marker-end: url(#edge-arrow);
+  }
+
+  rect {
+    fill: #F3F3F3;
+    stroke: #F3F3F3;
+  }
+  .Start, .End {
+    rect {
+      rx: 50%;
+      ry: 50%;
+    }
+  }
+  .Step {
+    rect {
+      fill: transparent;
+      stroke: transparent;
+    }
+  }
+  [data-status='error'] {
+    rect {
+      fill: #FFF0F1;
+      stroke: #FFF0F1;
+    }
+    &.Task text {
+      fill: #DA1E28;
+      font-weight: bold;
+    }
+    .chevron, .status-icon {
+      fill: #DA1E28;
+    }
+  }
+  [data-status='running'] {
+    rect {
+      fill: #EDF4FF;
+      stroke: #EDF4FF;
+    }
+    &.Task text {
+      fill: #282828;
+      font-weight: bold;
+    }
+    .status-icon {
+      stroke: #0062FF;
+    }
+    .chevron {
+      fill: #000000;
+    }
+  }
+  [data-status='success'] {
+    rect {
+      fill: #DAFBE4;
+      stroke: #DAFBE4;
+    }
+    &.Task text {
+      fill: #054719;
+      font-weight: bold;
+    }
+    .status-icon {
+      fill: #24A249;
+    }
+    .chevron {
+      fill: #0C5824;
+    }
+  }
+
+}