Install plugins from sidebar

Summary:
This diff adds "download" button to the plugins shown in "Detected in App" section, so they can be downloaded, installed and enabled just in one click.

For now UI is very simple - there is no progress indication and no error handling for failed downloads. I'll add them in next diffs.

Please note that we are explicitly "star" every installed plugin to enable it straight away without additional clicks in "disabled" section.

Reviewed By: mweststrate

Differential Revision: D25393472

fbshipit-source-id: 0a224ea6d03db0ee9a70b7fa35ede9616c03d824

desktop/app/src/reducers/connections.tsx

@@ -121,7 +121,10 @@ export type Action =
   | {
       // Implemented by rootReducer in `store.tsx`
       type: 'UPDATE_PLUGIN';
-      payload: PluginDefinition;
+      payload: {
+        plugin: PluginDefinition;
+        enablePlugin: boolean;
+      };
     };
 
 const DEFAULT_PLUGIN = 'DeviceLogs';
@@ -400,7 +403,10 @@ export const selectClient = (clientId: string | null): Action => ({
   payload: clientId,
 });
 
-export const registerPluginUpdate = (payload: PluginDefinition): Action => ({
+export const registerPluginUpdate = (payload: {
+  plugin: PluginDefinition;
+  enablePlugin: boolean;
+}): Action => ({
   type: 'UPDATE_PLUGIN',
   payload,
 });