Added marking queue, and made tutor clients callbacks.

Code cleanup. Been playing with a few different static code analysis ...

tools.  Used them to recommend the changes made in this commit.

Changed to mousePressed rather than mouseClicked because clicking labels is a ...

bit weird (seem less tolerant of movement during click than buttons).

Also attempting to fix problem with tutor client occasionally losing sync which
is probably due to threading (maybe server request thread deadlocking).

Stupid NetBeans random project file changes.

Improved TutorClient. Huge refactor. Icon now read from classpath/jar.

Initial commit.