JCLOUDS-686: Remove changesSince() query from base PaginationOptions

This PR deprecates the `changesSince(Date ifModifiedSince)` method in PaginationOptions. `changes-since` is specific to Nova (and [Glance](https://github.com/jclouds/jclouds-labs-openstack/pull/137)) and has moved to the Nova `ListOptions` class. 

Nova `ListOptions.maxResults(int maxKeys)` has been deprecated in lieu of `limit(int limit)`.

Updated tests updated and cleaned up a few doc links.

JIRA: https://issues.apache.org/jira/browse/JCLOUDS-686
Related PR for Glance: https://github.com/jclouds/jclouds-labs-openstack/pull/137
My preference would be for deprecated in 2.0 and remove in 2.1 but that's just me. We have no guidelines about the amount of time we allow users to deal with breaking changes. It's totally your call.