KNL-295 Allow caching of getAliases() in the AliasService.

The default size is 100,000 which is 10 times the default site size. This code is useful if you have page aliases being generated by the portal.

git-svn-id: https://source.sakaiproject.org/svn/kernel/trunk@133580 66ffb92e-73f9-0310-93c1-f5514f145a0a