Import pica plugin

Added plugin source code in org.goobi.production.plugin.opac package.

Added suitable filesystem structure:
…/plugins
…/plugins/command
…/plugins/import
…/plugins/step
…/plugins/opac
…/plugins/validation (for empty directories, see http://stackoverflow.com/questions/115983 )

Added jar file for Pica Opac

Updated description in goobi_config.properties