This commit repurposes AvatarAdapter and creates a new component, ImageAdapter, which accept an mxc uri and display the image represented by it, through FileHandler. It provides caching for the images, thus improves loading speed and enhances metadata privacy. It also makes the client better prepared for authenticated media.

Type: add

Verify unit tests pass.

In the room list view, verify avatars can be displayed.

Change the order of two rooms with different avatars (e.g. by sending a message to a room), and verify that the avatars are displayed properly.

Open the sticker picker with lots of stickers, and open it again in another room. Verify that the stickers load much faster.