* Only show repository avatar in list when one was selected

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Adds fallback configuration option for repository avatar

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Implements repository avatar fallback

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Adds admin task for deleting generated repository avatars

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Solve linting issues

Signed-off-by: Mario Lubenka <mario.lubenka@googlemail.com>

* Save avatar before updating database

* Linting

* Update models/repo.go

Co-Authored-By: zeripath <art27@cantab.net>