Context test tools (#168)

* add enzyme test helper with lingui provider

* add router context to enzyme test helper

* get 18n, router, & config contexts rendering together in enzyme helper

* add config context to enzyme helpers

* add network and dialog contexts to enzymeHelpers

* convert OrganizationForm tests to use new mountWithContexts helper

* default all context value keys to default unless provided

* document use of mountWithContexts()

* fix typo in CONTRIBUTING.md

* update Organizations to use mountWithContext

package.json

@@ -28,8 +28,9 @@
     "babel-loader": "^8.0.4",
     "babel-plugin-macros": "^2.4.2",
     "css-loader": "^1.0.0",
-    "enzyme": "^3.7.0",
-    "enzyme-adapter-react-16": "^1.6.0",
+    "enzyme": "^3.9.0",
+    "enzyme-adapter-react-16": "^1.12.1",
+    "enzyme-to-json": "^3.3.5",
     "eslint": "^5.6.0",
     "eslint-config-airbnb": "^17.1.0",
     "eslint-plugin-import": "^2.14.0",