feat: Introduce graphql image type

Created by: Tirokk

Authored by roschaefer Feb 12, 2020 Merged Mar 16, 2020

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🍰 Pullrequest

This is a first step to implement responsive images. We only refactor the schema here. Nothing needs to be uploaded, no files need to be moved.

Todo

• Implement and check user avatar file upload
• Double-check and fix image blurring
• Refactor code
• Check how many user.coverImg have survived our migration from alpha