Allow custom size (columns x lines) for SwingJediTerminal.

Hi Dmitry!

I'm facing the need to spawn a terminal with a custom number of columns x lines (as soon as the terminal is started; a resize after the spawn is not really acceptable).

I wrote this patch to modify `SwingJediTerminal` constructors to handle this need.
Do you think this can be a part of the JediTerm API and should be merged?

Thanks!
Clément