Support for creating new projects

* Add `create_project` and `project_name` parameters to `iron_core.IronClient`
* Update `iron_core.IronClient.request` to accept a full URL
* Don't overwrite `body` in `iron_core.IronClient.request`
* Append `Content-Type: application/json` header for POST requests

New behavior:
```python
>>> c = iron_core.IronClient(name="myclient", version="0.1", product='iron_mq', token='my-token-here', create_project=True, project_name='my-new-project')
>>> c.project_id
u'50fe1cfac570075220003e1b'
>>> c.base_url
u'https://mq-aws-us-east-1.iron.io:443/1/projects/50fe1cfac570075220003e1b/'
```