Add DB migration for recipient color preference.

// FREEBIE

src/org/thoughtcrime/securesms/database/DatabaseFactory.java

@@ -63,7 +63,8 @@ public class DatabaseFactory {
   private static final int INTRODUCED_UNIQUE_PART_IDS_VERSION  = 17;
   private static final int INTRODUCED_RECIPIENT_PREFS_DB       = 18;
   private static final int INTRODUCED_ENVELOPE_CONTENT_VERSION = 19;
-  private static final int DATABASE_VERSION                    = 19;
+  private static final int INTRODUCED_COLOR_PREFERENCE_VERSION = 20;
+  private static final int DATABASE_VERSION                    = 20;
 
   private static final String DATABASE_NAME    = "messages.db";
   private static final Object lock             = new Object();
@@ -742,6 +743,10 @@ public class DatabaseFactory {
         db.execSQL("ALTER TABLE push ADD COLUMN content TEXT");
       }
 
+      if (oldVersion < INTRODUCED_COLOR_PREFERENCE_VERSION) {
+        db.execSQL("ALTER TABLE recipient_preferences ADD COLUMN color TEXT DEFAULT NULL");
+      }
+
       db.setTransactionSuccessful();
       db.endTransaction();
     }