Fix and refactor launcher (part 1)

### Motivation
Improve the consistency and reduce the verbosity of the launcher; use `argparse` more aggresively. There will be about 3 or 4 PRs, each reducing the launcher size by about 100 lines.

### Changelog
* Fix various bugs and typos.
* Structure the parser arguments in a way that is easy to read and extend.
* Name the parser arguments, the `defaults` keys and the `OpenBazaarContext` atttributes with consistent names. Some flags are removed, others are renamed; consult the `usage` message.
* Reuse the `Namespace` object returned by the parser; it has all the default options built in.
* Remove execute flag from various `*.py` files.
* Remove outdated Windows script.
```bash
renelvon @ merchant ~/Repos/OpenBazaar (launcher_tidy) % python2
Python 2.7.6 (default, Mar 22 2014, 22:59:56) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from node import openbazaar
>>> a = openbazaar.create_argument_parser()
>>> res = a.parse_args(['start'])
>>> res.server_ip
'127.0.0.1'
>>>
```