Show offline devices in dropdown

Summary:
This diff aims to make the selected device a little clearer, the button now shows different icons depending on the selected devices: physical, emulators and archived devices.

The dropdown now is grouped in these sections, depending on their availability:
- Connected Devices
- Running Emulators
- Imported Devices
- Launch Android emulators
- Open File...

"Open File..." allows to import a file the same way as File -> Open File...

Reviewed By: jknoxville

Differential Revision: D14460789

fbshipit-source-id: 8d6edff0d90d5e02e4ef5976af5680ab8eaf77b4

src/utils/icons.js

@@ -35,6 +35,14 @@ export const precachedIcons: Array<string> = [
     name: 'mobile',
     size: 12,
   },
+  {
+    name: 'box',
+    size: 12,
+  },
+  {
+    name: 'desktop',
+    size: 12,
+  },
   {
     name: 'bug',
     size: 12,