Separate dev and metadata volunteers in status JSON

Updated ``State.status_entry()`` to output separate lists of
dev and metadata volunteers.

Fix syntax of mock dependency in requirements-dev.txt

Addresses https://github.com/openelections/dashboard/issues/28
DRY up State.results_status() implementation
Add "partial" (in-progress) value to results_status

Update State.results_status to return a value of 'partial' if
there has been a volunteer developer associated with the state.

While the status will be displayed as "In-progress" on the front
end, we're using the "partial" value to match the options for
the metadata_status field.

Addresses https://github.com/openelections/dashboard/issues/29,
https://github.com/openelections/openelections.github.io/issues/19
Merge pull request #30 from openelections/update_front_end_metadata

Update front end metadata JSON baking

Update State model methods used to create the JSON files that drive the status map and table on openelections.net.

Create separate lists of development and metadata volunteers.

Add a 'partial' status for state election results that reflects whether or not a development volunteer has been assigned to the state.