Fix: handling for ISO topic keyword.  Added IsoTopicResolver to handle
ISO topic keywords for FGDC and OGP metadata parsing.  Removed ISO topic
from the Solr record model, since the schema does not support it.

Also, fixed handling of scanned maps to report as "raster" type.
Merge pull request #70 from chrissbarnett/remove_topic

Fix: handling for ISO topic keyword.  Added IsoTopicResolver to handle