make application Python 3 compatible

Upcoming changes introduce functionality more easily implemented using
Python 3. Also, the only reason for sticking to Python 2 was that the
oandapy module was not runnable with Python 3.
Now that oandapy was converted to run on Python 3, this change converts
fxBot to use Python 3 as well.
MERGE W/ 6614e0b6
MERGE W/ 5f1dffa0