Add support for 'last' function
Add support for 'last' function

'last' function is supported in monasca,
therefore UI should allow to contruct expressions
with it

Implements: Blueprint last-value
Change-Id: I228b7aa4e1e724a469b4cfa455f3199d879bb0ac

stackforge/monasca-ui,openstack/monasca-ui,stackforge/monasca-ui,stackforge/monasca-ui,openstack/monasca-ui,openstack/monasca-ui,openstack/monasca-ui,stackforge/monasca-ui