Added .pymop.log to gitignore in the test astromdir.
Added ability to reset the colormap of an image back to default levels.
This is done using a keystroke as specified in the application config file 
(currently 'c').
Changed keybind for resetting colourmap to 's'.
#38: colourmap starts out reversed so that black is high and white is low.
Made circle around source blue instead of yellow to improve 
visibility on images where the colourmap has been inverted (which 
happens by default now).
Merge pull request #40 from drusk/invert_colormap

Colormap adjustments