DEV-39188: Removed the custom support for secondlife:///app/events and

secondlife:///app/classifieds URLs because we do not have handlers for
these SLAPPs in 2.0.

Added support for secondlife://<location/<x>/<y>/<z> URLs, in addition
to the http://slurl.com SLURLs.

Also optimized LLUrlRegistry:findUrl() so that it avoids lots of
expensive regex calls when there is no URL in the text.