Add new handling to encourage the user to save their wallet recovery phrase.

This only effects those who have opted in to payments and have a non-zero balance.

libsignal/service/src/main/java/org/whispersystems/signalservice/api/payments/Money.java

@@ -68,6 +68,8 @@ public abstract class Money {
 
   public abstract boolean isNegative();
 
+  public abstract boolean isEqualOrLessThanZero();
+
   public abstract Money negate();
 
   public abstract Money abs();
@@ -147,6 +149,11 @@ public abstract class Money {
       return amount.signum() == -1;
     }
 
+    @Override
+    public boolean isEqualOrLessThanZero() {
+      return amount != null && amount.compareTo(BigInteger.ZERO) <= 0;
+    }
+
     @Override
     public MobileCoin negate() {
       return new MobileCoin(amount.negate());