Fix photo & camera permission management (#140)

* Check photo & camera perms and alert the user if not available (close #64)

- Adds perms checks with a prompt to update settings if needed
- Moves initial access of photos in the composer so that the initial prompt
  occurs at an intuitive time.

* Add react-native-permissions test mock

* Fix issue causing multiple access requests

* Use longer var names

* Update podfile.lock

* Lint fix

* Move photo perm request in composer to the gallery btn instead of when the carousel is opened

src/state/models/user-local-photos.ts

@@ -20,7 +20,7 @@ export class UserLocalPhotosModel {
   }
 
   private async _getPhotos() {
-    CameraRoll.getPhotos({first: 20}).then(r => {
+    return CameraRoll.getPhotos({first: 20}).then(r => {
       runInAction(() => {
         this.photos = r.edges
       })