reaction display misinterprets reversibility

Instead of explicitly looking for 0 or 1, the arrow is now set by
evaluating if self.reversibility as expected. This makes the reactions
display correctly with the reversibility property
Merge pull request #42 from aebrahim/reaction_display_fix

reaction display misinterprets reversibility
Reaction.boundary is now a property

If a reaction has only a single metabolite or it ONLY consumes or
produces metabolites, it is a system boundary
Remove depracated functions
update pickles
Merge branch 'master' of github.com:opencobra/cobrapy into reaction_clean
remove _boundary_metabolites
Merge pull request #43 from aebrahim/reaction_clean

Clean up Reaction class
Update to latest python in INSTALL.md

now point to 2.7.6 instead of 2.7.3
Merge pull request #4 from opencobra/master

Pulling in patches from opencobra:master