Moves sources from columns to footnotes

Adds a sources table at the bottom of the results
footnote numbers don't start at 1, they simply use the source_reference
id
Make source reference numbers start at 1 and increase
Simplify source_references

Remove names, year, and URL.  Rename title to source
Updates to handle simplified source_references table

Using :source field instead of to_s or title
Removed URI logic and string_to_hash method from validator
Add 'Sources' label to table
Merge pull request #55 from NESCent/sources_to_footnotes

Sources to footnotes