Show feedback while picking/processing a video, and then again while encrypting/uploading it

When I pick a video, it looks like it failed. But if I wait, the video appears and I can upload it.

We need to show the user that the app is working, or they will give up.

Similarly, when I tap the button to send the post, the button itself grays out but the rest of the composer still looks like it's active. We should shade the whole composer and show some sort of progress view.