2 small bugs found using Python 2.7.12

[henrietteschwarz]

In wavelength_utils.py function twodfit()
pandas.DataFrame.icol has been deprecated http://pandas.pydata.org/pandas-docs/version/0.19.2/generated/pandas.DataFrame.icol.html.
Solution: Replace .icol(i) with .iloc[:, i]

In image_lib.py function cut_out()
Python complained that slice indices must be integers.
Solution: Place int() around both 'top' and 'bot' everywhere in the function.

After implementing the above 2 solutions, everything ran smoothly.