Python b64 encoder

Currently all the ARCH_PYTHON payloads are base64 encoding themselves. Ideally we implement an encoder that handles this kind of thing. 

Poke @zeroSteiner The bind_tcp and reverse_tcp stagers currently do some advanced stuff that I'm not sure is required or not?

You can execute \t statements in an exec statement e.g. `exec("if True:\n\tprint 1")` the \t is probably only a badchar for the commandline?

== Verification ==
- [ ] python/meterpreter/reverse_tcp and bind_tcp still work
- [ ] python/shell_reverse_tcp and shell_reverse_tcp_ssl still work
- [ ] Check for modules with ARCH_PYTHON and sort out badchars...