Added ability to load spectra from files.

 - Added option to select an image from another Android app for the
   baseline or sample image (works best with apps like Dropbox or a file
   viewer, doesn't always work with the built in Gallery app).
 - Fixed a bug regarding the screen location of a point compared to the
   logical location of a point -- absorbance and sample images were not
   properly scaled to the screen width.
 - Made the points larger and much easier to see on the screen.