Monopoly(r)+Release+3+Player+Pays+Back+Mortgage

As a Player, I can pay back the mortgage on a property.

User Acceptance Tests

 * Player pays for mortgage. Player's balance decreases by 100% of the property value. Property no longer mortgaged.
 * Player tries to pay for property that is not mortgaged. Fails.
 * Player tries to pay for property that is not owned. Fails.
 * Player tries to pay for property they do not own. Fails.

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