Display a generated avatar icon rather than a single default.

If the contact doesn't have an image, render a color-coded
background and the first letter of the contact's name.

1) Don't display anything during recipient resolution.

2) Display a # icon in material gray for recipients with no name.

3) Display a material group icon in material gray for groups with
   no avatar icon set.

Closes #3104

// FREEBIE

src/org/thoughtcrime/securesms/jobs/AvatarDownloadJob.java

@@ -2,6 +2,7 @@ package org.thoughtcrime.securesms.jobs;
 
 import android.content.Context;
 import android.graphics.Bitmap;
+import android.graphics.drawable.BitmapDrawable;
 import android.util.Log;
 
 import org.thoughtcrime.securesms.Release;
@@ -74,7 +75,7 @@ public class AvatarDownloadJob extends MasterSecretJob {
 
         Recipient groupRecipient = RecipientFactory.getRecipientsFromString(context, GroupUtil.getEncodedId(groupId), true)
                                                    .getPrimaryRecipient();
-        groupRecipient.setContactPhoto(avatar);
+        groupRecipient.setContactPhoto(new BitmapDrawable(avatar));
       }
     } catch (InvalidMessageException | BitmapDecodingException | NonSuccessfulResponseCodeException e) {
       Log.w(TAG, e);