GIF Support - EditPostSettings

[malinajirka]

Fixes #7967

Replaces Volley with Glide in the EditPostSettings.
Adds support for adding animated feature images.

To test:

1. Click on the create post button

2. Type any title

3. Click on three dots in the top right corner of the screen

4. Click on Post Settings

5. Click on the Set feature image button

6. Select any GIF image

7. Notice the animation is working and click on the Publish button

8. Go to Reader - Followed Sites

9. Make sure the post has animated GIF image

[malinajirka]

@oguzkocer I changed the size of the feature image preview. Previous implementation was using 'thumbnail', which has quite a low quality. Current implementation uses the full image and optimizes it using Photon.

[malinajirka]

I'll create another PR when #7976 is merged and the code is ready for review.