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>
As mentioned in my [previous comment](https://github.com/cbmi/avocado/pull/212#discussion-diff-15399503), the field type needs to be checked to ensure it is only an enumerable or key-base field. The list-based value below is the case where handling a number/data/time/large text would be suboptimal due to the unnecessary lookup for the value.