Porting to python 3

[sulheim]

Is there any plans of porting metdraw to python 3?

[dsurujon]

I made the following quick changes to get it to work with Python 3:

• Fix all print statements in metdraw.py, model.py, sbml.py to have parentheses
• There's no need to convert unicode to str in Py3. So in util.py line 18, you should have unicode_to_str=False
• In sbml.py line 78 the variable notes can be None. Handle this with an if/else statement

	if notes == None: notetext = ""
	else: notetext=ET.tostring(notes)

• In gpr.py line 33, open the file with wb instead of w
• In layout.py replace all occurences of rids.next() with next(rids)

You can find it in my forked repo here. Hope it helps!