Things added
- functionality for background subtraction  by manually select points, fit a spline and subtract
- output of all datasets to a .xyz output file
- reset button added to clear out all datasets and plots
- function to add an offset and multiplier to both x and y axes
background removal routines added using gsas fitting code
basic peak finding and fitting also included
individual peak selection added
labels on peaks added
ability to export a fitted background and save peak parameters added
bug fixes and some tests, committing all changes before merging back to master
Merge branch 'background_subtraction'