Adjusting uploaded avatar images to be cropped and scaled
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Issue idea came from: gitlab-ce#28158
#### Problem
People right now have to pre-edit their images to be the correct size and aspect ratio in order for it to end up in a good state as an project or personal avatar. Services such as facebook, google, etc show us that this should be done automatically by a plugin of some sort.
#### Proposal
Implement an uploaded image adjuster that crops, scales and sets a certain aspect ratio.
examples:
- https://tympanus.net/codrops/2014/10/30/resizing-cropping-images-canvas/
- http://scottcheng.github.io/cropit/
- http://www.croppic.net/
#### Value
- Less irritation
- easier avatars
#### Related issues
gitlab-ce#28158
cc: @jschatz1 @nmrony
issue