Include more readable information in status monitor "error log" section

* Don't print an exception's message twice. Instead, just print the exception's message. If there is no message, print the class name.
* Set a new "stackTrace" key on deposit status hashes with the stack trace from the exception.
* Display the stack trace in the status monitor (with monospaced font)
Merge pull request #212 from UNC-Libraries/status-monitor-error-messages

Include more readable information in status monitor "error log" section