First pass at Iowa datasource

I still need to preprocess the PDF data and wire this in.

Addresses https://github.com/openelections/core/issues/118
Remove incorrect entry for 2010 general election results

The row for the 2010 primary results file was duplicated for the
general election.

Addresses https://github.com/openelections/core/issues/118
Set the reporting level for the 2010 general results file

I forgot to do this in the last commit.

Addresses https://github.com/openelections/core/issues/118
Merge branch 'dev' into 118-ia_datasource

Bring this feature branch up-to-date
Add 2014 primary election results to datasource

* Add 2014 county-level PDF to url_paths.csv
* DRY up logic that creates mappings for precinct-level Excel results for elections in 2006 onward
* Update _precinct_xls_metadata to use .xlsx extension for elections starting in 2014
* Add jurisdiction column to url_paths.csv and use it in the canonical filename.  This was needed because there are per-county, precinct-level results for some special elections

Addresses #118
Wire in preprocessed Iowa results into datasource

Now that the bulk of Iowa's PDF results have been converted to
CSV, point the datasource at the CSV versions on GitHub.

Addresses #118
Merge pull request #200 from ghing/118-ia_datasource

Add Iowa datasource