[Jupiter] Refactor thumbnail generation code

[murny]

Noticed this when working on this issue: #982.

Some refactors could be had here. We basically got 5 places where thumbnail generation happens (communities, items, theses, draft items and draft theses). Some are done in the model, others done in the view. Lots of repeated code across the application.

These two views for example are exactly the same:
https://github.com/ualbertalib/jupiter/blob/c88f89cabb034deac19f0872c1d41e4d2ea4103b/app/views/admin/theses/draft/_thumbnail.html.erb
https://github.com/ualbertalib/jupiter/blob/c88f89cabb034deac19f0872c1d41e4d2ea4103b/app/views/items/draft/_thumbnail.html.erb

These code blocks are pretty similar:

jupiter/app/models/community.rb

Lines 32 to 37 in c88f89c

	# compatibility with item thumbnail API
	def thumbnail_url(args = { resize: '100x100', auto_orient: true })
	return nil if logo_attachment.blank?
	Rails.application.routes.url_helpers.rails_representation_path(logo_attachment.variant(args).processed)
	end

jupiter/app/models/concerns/draft_properties.rb

Lines 48 to 59 in c88f89c

	# compatibility with the thumbnail API used in Items/Theses and Communities
	def thumbnail_url(args = { resize: '100x100', auto_orient: true })
	return nil unless thumbnail.present? && thumbnail.blob.present?
	Rails.application.routes.url_helpers.rails_representation_path(thumbnail.variant(args).processed)
	rescue ActiveStorage::InvariableError
	begin
	Rails.application.routes.url_helpers.rails_representation_path(thumbnail.preview(args).processed)
	rescue ActiveStorage::UnpreviewableError
	return nil
	end
	end

jupiter/app/models/concerns/item_properties.rb

Lines 62 to 73 in c88f89c

	def thumbnail_url(args = { resize: '100x100', auto_orient: true })
	logo = files_attachment_shim.logo_file
	return nil if logo.blank?
	Rails.application.routes.url_helpers.rails_representation_path(logo.variant(args).processed)
	rescue ActiveStorage::InvariableError
	begin
	Rails.application.routes.url_helpers.rails_representation_path(logo.preview(args).processed)
	rescue ActiveStorage::UnpreviewableError
	return nil
	end
	end

Be nice if we could DRY up a lot of this duplicated code (maybe move it into a concern/helper etc?). Or just reevaluating what this code does and why we need it in the model etc? Maybe we can all share the same thumbnail partial everywhere?

[mbarnett]

Think this is now being tracked on #1343