Allow datacontext to return the real values for concepts and filters

![screen shot 2014-05-29 at 11 06 52 am](https://cloud.githubusercontent.com/assets/2774472/3119075/eb405cf4-e742-11e3-936a-7edb45d6961d.png)

What is returned when a filter is applied.

This will be used to apply styles to the filter display in filter.js 

Signed-off-by: Sheik Hassan <solergiga@yahoo.com>
@hassanNS Just reviewed this again. As far as I know the only possible values can be `QuerySet` instances, `Model` instances, or primitive values. Do you mind changing this portion to a separate `elif` block:

```python
# Add import above..
from django.db import models

...
elif isinstance(value, models.Model):
    cleaned = {'value': value.pk, 'label': value_labels[value.pk]}
...
```

This should remove try/except portion of this block.