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

src/contexts/Network.jsx

@@ -82,4 +82,3 @@ export function withNetwork (Child) {
     </NetworkContext.Consumer>
   );
 }
-

src/contexts/RootDialog.jsx

@@ -16,7 +16,8 @@ export class RootDialogProvider extends Component {
         clearRootDialogMessage: () => {
           const { value } = this.state;
           this.setState({ value: { ...value, title: null, bodyText: null, variant: null } });
-        }
+        },
+        ...props.value,
       }
     };
   }