Stop Fitting

Testing functionality to stop the fitting.
recommit files more cleanly

Removed extra code, extra files from previous commit.
add stop fitting functionality

DREAM, DE, Quasi Newton and Amoeba can be stopped in the middle of
fitting through the GUI.
use 'with' keyword

Replaced acquiring and releasing thread locks with the 'with' keyword.
Merge pull request #2 from ScottSWu/master

stop button