Add better exception handling
Add better exception handling

Unhandled exceptions before this commit:
- error code 500
- generic error message as HTML: "<html><body><h1>Custom 500 handling</h1></body></html>"
- Nothing printed out on the server

Unhandled exceptions after this commit:
- error code 500
- specific error message as JSON: '{ "exception" : "class java.lang.NullPointerException", "message" : null }'
- on the server we print out
  + date, with generic message
  + verb (GET, PUT, etc), with full URL and query string
  + full stacktrace

issue #7

UMM-CSci-3601-S17/digital-display-garden-iteration-4-dorfner-v2,UMM-CSci-3601-S17/digital-display-garden-iteration-4-dorfner-v2,UMM-CSci-3601-S17/digital-display-garden-iteration-4-dorfner-v2,UMM-CSci-3601-S17/digital-display-garden-iteration-4-dorfner-v2,UMM-CSci-3601-S17/digital-display-garden-iteration-4-dorfner-v2