Replace avatars by dragging images into the avatar field.

#### Is your suggestion related to a problem? Please describe.
When quickly wanting to change a room avatar to some picture someone posted somewhere (in element or the web) I first need to save the picture, open it with gimp, crop it to some reasonable dimensions, save it again and then upload it as an avatar.

#### Describe the solution you'd like
Dragging an image over the old avatar to replace it (or similar).

#### Alternative
Instead I want to just copy the image or parts of it (gnome quick selection tool or windows snipping tool) to the clipboard and paste it into element as a new room avatar, saving all of the intermediary steps above.