Modal pager

Summary

Go back and forth on images/videos/blogs for the current user or group on media modal.

Closes #1737 (closed). Depends engine!437 (merged)

Steps to test

• Visit https://epic-modal-pager.minds.io/0xemi/. Arrows will appear in the main view to allow going back and forth all user's media.
• Log in with your user
• Post 2 or more images or blogs (video transcoder seems to be down for review sites)
• Click one of them, you should be able to go back and forth using the arrows (keyboard/on-screen element)
• Test that you are able to close the media modal using Esc key.
• Test that when you use the keyboard arrows on text fields (i.e. the comment input) it doesn't trigger the navigation
• Go to a group (or create a new one), copy the URL
• Post a couple of images
• Login with another user (or create a new one)
• Go to the group and join it
• Post a couple of images
• Test that you can go back and forth all groups images on the media modal.

Estimated Regression Scope

• Media modal entity loading
• Media modal media sizing
• Media modal permalink URLs