python templates need access to more data from stack_config

[1oglop1]

Currently only sceptre_user_data is passed to sceptre.Template
https://github.com/cloudreach/sceptre/blob/master/sceptre/stack.py#L203

and then passed to sceptre_handler
https://github.com/cloudreach/sceptre/blob/master/sceptre/template.py#L129

This leads to lose relation between template and stack config.
E.G:
stack_config.yaml

parameters:
  VpcId: 1234
sceptre_user_data:
  SecurityGroups:
  - sg-1234

Currently every templates needs to implement sceptre_handler method
template.py

import troposphere as tr

def sceptre_handler(sceptre_user_data):
   # from here the template developer has access only to  sceptre_user_data
   # if stack_config contains parameters developer needs to create them without having any reference to the stack config
   tmplt = tr.Template()
   tmplt.add_parameter(tr.parameter(Parameter('VpcId'))
  # but properties of resources could be loaded from stack config via sceptre_user_data
   tmpl.add_resource(tr.ec2.SecurityGroup('sg', **sceptre_user_data['SecurityGroup'])

Possible quick fix is to add parameters and other data passed to the Template.
Another way is to refactor the approach how the templates are being created.