Rewrite std_dev_across_tracts

- Now takes a list of target columns to be summed
- Renamed, cleanup, PEP8
Generator for returning real and fake boundaries
Add metric detail view, alter score view

- Metric detail is specified by the boundary and the node slug.
- Score view drops citations, changes references to boundaries,
  and adds URI to detail view
- New boundary view for fake boundaries
- Algorithms refactored to allow scoring by location or boundary
- Census algorithms refactored for common code

Also
Drop ScoreMetric fields

These fields make dumpdata / loaddata harder, but are unused in the
code and not used for documentation.  Use params until we have a
better idea what the score model will be.
Merge pull request #21 from jwhitlock/metric_refactor

Metric refactor
Merge harbieism, pep8 pass
Refactor algorithms into CensusPercentAlgorithm
Remove duplicate REST_FRAMEWORK setting
Merge pull request #22 from jwhitlock/harbieism

Integrate harbieism's new census algorithms
Discard census rows with zero or null in total columns
Return placeholder data for census algorithms w/o boundaries
Add score details to census data via metric params
Add total score at top level of score API
CensusPercentAlgorithm.get_stats: fix bug if no stats override
Sync placeholder score_text with census score_text
Add new scores.json, instructions for generating
If boundary doesn't have census data, return placeholder details
Add access to jobs
Add Employment Status
Add High School Graduation Rate