Added basic pagination features in template list

Added basic pagination features in template listings.
There is still pending the global refactor to adapt every paginated call
to the PagedIterable. This commit just makes the
VirtualMachineTemplateOptions class support the Abiquo pagination query
parameters.
Added allowed tiers feature to Abiquo

Abiquo 2.4 introduces a new feature to allow platform administrator to
configure the visibility of the storage tiers for each tenant, in order
to have more control over the storage resources usage.
Fixed allow datacenter