Invalid date string in iso2geoBL.xsl

[waynegraham]

Running the iso2geoBL.xsl transform on metadata from GeoNetwork produces a Solr doc that is rejected with the following response:

RSolr::Error::Http - 400 Bad Request
Error: {'responseHeader'=>{'status'=>400,'QTime'=>1},'error'=>{'msg'=>'Invalid Date String:\'2010-11-08\'','code'=>400}}

This appears to be in the layer_modified_dt field. I believe this requires a full timestamp.

https://github.com/geoblacklight/geoblacklight-schema/blob/master/conf/schema.xml#L72

https://cwiki.apache.org/confluence/display/solr/Working+with+Dates

May need to update https://github.com/OpenGeoMetadata/GeoCombine/blob/master/lib/xslt/iso2geoBL.xsl#L218-L229

So the fallback can generate a fake timestamp (maybe with xs:time?).