WFLY-406 Redesign web session clustering

Implementation notes:
* Web session clustering SPI and Infinispan provider are completely new, hence the migration to the org.wildfly.clustering.web.spi and org.wildfly.clustering.web.infinispan packages, respectively.
* Web session clustering container integration code for JBoss Web and Undertow now resides in clustering/web/catalina and clustering/web/undertow, respectively.