Made some inner classes static (For Efficiency)

(and made one explicitly private)

Closes #3932
// FREEBIE

src/org/thoughtcrime/securesms/util/CharacterCalculator.java

@@ -20,7 +20,7 @@ public abstract class CharacterCalculator {
 
   public abstract CharacterState calculateCharacters(int charactersSpent);
 
-  public class CharacterState {
+  public static class CharacterState {
     public int charactersRemaining;
     public int messagesSpent;
     public int maxMessageSize;