Show avatars on message notifications

[Goooler]

Closes #7089.

[Goooler]

This needs to be called on minSdk 23, the current is 21. We have to bump the minSdk or update

thunderbird-android/legacy/ui/legacy/src/main/java/com/fsck/k9/contacts/ContactPictureLoader.kt

Lines 59 to 69 in f262b0a

	@WorkerThread
	fun getContactPicture(recipient: Recipient): Bitmap? {
	val contactPictureUri = recipient.photoThumbnailUri
	val address = recipient.address
	return if (contactPictureUri != null) {
	getContactPicture(contactPictureUri)
	} else {
	getFallbackPicture(address)
	}
	}

to accept a Transformation for CircleCrop for avatars.

[asoucar]

Thanks for working on this! We're going to run this by design before reviewing but then we'll get back to it