GEOMESA-491 Add ability for Geoserver plugin to scan multiple columns

Changes plugin wms layer configurations to allow for a list of columns to scan
GEOMESA-488, 492 Understand and remove use of jai_core, CoverageReader's VersioningIterator's random name string isn't created properly

Excluded jai_core and removed usages of jai_core functionality from geomesa-plugin. Also
fixed an issue with a random name not being properly generated for VersioningIterator
in CoverageReader