feat(Compose): exclude own account from reblog mentions

Excludes the users account from being automatically included when
repplying to a status that has been bosted by the user.

Fixes #548

mastodon/src/main/java/org/joinmastodon/android/fragments/ComposeFragment.java

@@ -787,7 +787,7 @@ public void getOutline(View view, Outline outline){
 			String ownID=AccountSessionManager.getInstance().getAccount(accountID).self.id;
 			if(!status.account.id.equals(ownID))
 				mentions.add('@'+status.account.acct);
-			if(status.rebloggedBy != null && GlobalUserPreferences.mentionRebloggerAutomatically)
+			if(GlobalUserPreferences.mentionRebloggerAutomatically && status.rebloggedBy != null && !status.rebloggedBy.id.equals(ownID))
 				mentions.add('@'+status.rebloggedBy.acct);
 			for(Mention mention:status.mentions){
 				if(mention.id.equals(ownID))