[WIP] Fix "Can't edit shared image" (#2034)

Fix #2032

The problem was that after returning from the image editor, `doReinitializeDraft` was true and therefore we the draft was reinitialized to the originally shared, unedited image.

This was introduced in
https://github.com/deltachat/deltachat-android/pull/1770. I im pretty
sure that what I changed is fine, but we had so many regressions in the
past in this area that we should thoroughly test this change before
merging.

I extended
https://github.com/deltachat/interface/edit/master/user-testing/mailto-links.md
a bit; before merging this PR we should test that everything there still
works.

src/org/thoughtcrime/securesms/ConversationActivity.java

@@ -429,6 +429,7 @@ public class ConversationActivity extends PassphraseRequiredActionBarActivity
       break;
     case ScribbleActivity.SCRIBBLE_REQUEST_CODE:
       setMedia(data.getData(), MediaType.IMAGE);
+      doReinitializeDraft = false;
       break;
     case SMS_DEFAULT:
       initializeSecurity(isSecureText, isDefaultSms);