Support for templated RPC requests.

This starts out by creating a new route for /v2 of our API. This
supports sending a list of Nodes with arbitrary facts that can be used
with templates as part of the RPC request. See the documentation for
additional details.
Break out the actual result logic to new function.

This allows us to manipulate requests prior to sending the raw RPC
request. An example of this is the new NetconfTemplateWorker which uses
the text/template library to allow templating.
Factor out as much handler logic as possible.

This is a first pass at simplifying the handler logic enough to move it
into one simple function.
Add comments and order code appropriately.
Namespace our v2 NETCONF handler to /v2/netconf.
Make sure we initialize NetconfResult
Error recovery and add a validation route
Some cleanup
add a note about template support