See #1100: clean compat and XXX in the code

• Use attachment.urls.<image_size> instead of attachment.<image_size>
• Removed Full text search setting, it's now on by default
• Generated some missing migrations
• Removed nested users/users api
• Removed some unused settings
• Remove actor field in federation collection, in favor of attributedTo
• Remove cover field in federation album representation, in favor of image