mimic the main() method instead of deprecated Main() class of gprof2dot

see
https://code.google.com/p/jrfonseca/source/detail?r=bf25a2abb09bf2cb821832d76900f0dd8326eb8a&repo=gprof2dot

for more info on this change of gprof2dot.

The main method is copied, except the optparser part that reads from
sys.arg. The output of optparser is replaced by an empty Options class
populated with hard-coded options.

Only gprof2dot imports to a limit number of classes, attributes were made.
pip install specific commit of gprof2dot

The use of gprof2dot in RMG-py is tailored to the version of gprof2dot
contained in this commit.

To prevent people with older versions of gprof2dot to run into problems,
we checkout this commit specifically.
Tweaks gprof2dot implementation.

1. Change the wording in the warning when the import fails. 
   (To suggest a different version).
2. Prevent a ton of PostScript warnings when running dot on MacOS X
   (calling a font by the wrong name).
3. Remove an out of date comment
Update URL to Oasa library in requirements.txt
Remove Oasa library from requirements.txt

This is no longer needed.