Made location optional in ISOCode
Update load.py to read ISO Codes from ethnologue

Fixes #40
load languages from 17th Ed Missing ISO codes

Implements #47
Update load_all_datasets.sh for reading iso/langs

See #40 and #47
Fix bug in rendering LanguageClassification as unicode
Merge pull request #48 from NESCent/read_iso_codes_ethnologue

Updates to reading ISO Codes and languages
Rename EAVariableDescription to VariableDescription
fix verbose name of VariableDescription
Migration for renaming EAVariableDescription
Rename EAVariableCodeDescription to VariableCodeDescription
Migration for renaming EAVariableCodeDescription
Rename EAVariableCodedValue to VariableCodedValue
Migration for renaming EAVariableCodeValue
Propagate name changes to tests
Add Source model
Migration for adding Source
Change variable number to label, add source FKs
Migration for changing number to label
Update tests to use variable.label instead of variable.number
Update load.py to change variable number to label