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
> This option is deprecated in jclouds 2.0 and will be removed in jclouds 3.0

For now, while we still consider X.Y a major and X.Y.Z a minor version, I guess that should be "deprecated in 1.8 and removed in 2.0" or "deprecated in 2.0 and removed in 2.1", indeed.