Allow group owners to upload a banner image for a group and edit a group name/description

[meghanmae]

Relies on #5

• Display & load the name, description and banner/profile image of a group
• You'll also need to write some code to allow uploading and downloading images (use IFile, docs here: https://intellitect.github.io/Coalesce/modeling/model-components/methods.html#other-file-storage)
  • Similar work to Display an org's description name and banner image #8
• Allow the owners of the group AND owners of the org a way to edit these things