http://blog.danlew.net/2015/10/07/sharing-files-on-android-in-a-world-with-runtime- permissions/ • https://medium.com/ribot-labs/exploring-the-new-android-permissions-model- ba1d5d6c0610 • https://commonsware.com/blog/2015/10/07/runtime-permissions-files-action-send.html • https://github.com/tbruyelle/RxPermissions