ENH: parallel context

Currently don't have support for mapping yet, but we can submit system calls or function calls now via IPython. The latter may require state updates on the engines, which is feasible from the current context. It is likely that mapping will go in relatively easily. 

From the shell:

```bash
$ echo -e "profile\tdefault" >> ~/.qiime_config
$ echo -e "n_engines\t2" >> ~/.qiime_config
$ parallel start
```

From within Python:

```python
>>> from qiime.parallel.context import context
>>> context.submit_sync('hostname')
('rl1-1-220-221-dhcp.int.colorado.edu\n', '', 0)
>>> def foo():
...     return "bar"
...

>>> context.submit_sync(foo)
'bar'
>>> def foo(a):
...     return a**2
...
>>> res = context.submit_async(foo, 5)
>>> res.result
25
```

From the shell:

```bash
$ parallel stop
```
Can we ensure this version is compatible with other dependencies?

On (Oct-07-14|11:12), josenavas wrote:
> > @@ -256,6 +256,9 @@ def app_available(app_name):
> >        keywords=['bioinformatics', 'microbiome', 'microbiology', 'qiime'],
> >        platforms=['MacOS', 'Linux'],
> >        install_requires=['numpy >= 1.7.1',
> > +                        'click >= 1.0',
> 
> Checked on my end and seems to work
> 
> ---
> Reply to this email directly or view it on GitHub:
> https://github.com/biocore/qiime/pull/1616/files#r18537889