Ticket129: Fix resource leak

Add try...finally statement to BBCTFrame.readCards() to make sure that
the file is closed.
Ticket 129: Remove unused import statements
Ticket 129: Remove `import junit.framework.Assert;`

`junit.framework.Assert` is deprecated in favor of `org.junit.Assert`.
Ticket 129: Suppress serialization warnings

Suppress the warning "The serializable class does not declare a static
final serialVersionUID field of type long" for classes which will never
be serialized.
Ticket 129: Add `serialVersionUID` to `BaseballCard`