resource/gitlab_topic: Support avatars
This change set introduces avatar support for topics.
To reliably detect changes in the avatar the avatar is hashed into the internal _avatar_hash
attribute and a custom diff function is used to detect changes in the avatar if the filename stays the same.
I thought about comparing against the image returned from avatar_url
, however I doubt that this would be reliable enough because the image might be changed slightly - e.g. cropped or compressed - especially when gravatar is used.
@armsnyder wdyt about this solution?