Implement and use WeakRedrawTimer to avoid memory leak
Make WeakRedrawTimer static

Non-static inner class automatically have an implicit reference to the
containing instance.
This is preventing enclosing TerminalPanel to be garbage collected.
Stop ExecutorService in close()

As long as ExecutorService is not shut down, spawned threads are not
cleared. This is memory leak prone.
Merge pull request #37 from Plonk42/timer_leak

Fix memory leak when JediTerm is used in another application