Add Implementation of MissingObject

Adds an implementation of the MissingObject class so that the MissingObjectProxy
can demonstrate dynamic loading (rather than Dynamic Linkage). MissingObject is
the same as ExpensiveObject. We delete its .class file after building to demonstrate
that classes are only loaded when the constructor is called.

Added:

 * MissingObject.java
Clean Up Code of ExpensiveObject

Collapses the empty method bodies in ExpensiveObject.

Changes:

 * ExpensiveObject.java
Don't Use Dynamic Linkage in Proxies

Modifies ExpensiveObjectProxy and MissingObjectProxy so that they don't use Dynamic
Linkage, instead creating the proxied objects directly using their constructor.
(Follow the instructions, dummy.)

Changes:

 * ExpensiveObjectProxy.java
 * MissingObjectProxy.java
Bring Back Driver's status Variable

Brings back the driver class's status instance variable, so that the status
string can persist across screen refreshes.

Changes:

 * VirtualProxyDriver.java