Added ``data`` as optional JSONField to extra price models.
Added requirement jsonfield
jsonfield>=0.9.4 does not support plain strings, therefore restricted to version 0.9 and 0.9.2
whitespace
added test with unicode strings
Merge branch 'master' into add-data-to-extra-price-fields
Bumped required package jsonfield to version 0.9.6
Merge pull request #216 from jrief/add-data-to-extra-price-fields

Added ``data`` as optional JSONField to extra price models.