Methods for new "maps" property in TD Root

Methods for new "maps" property in
Template Data JSON root added to
the Template Specification Model

* Added maps property to MWTemplateSpecModel
* Maps filled in extend function
* Added getter function for maps

Depends on I3bf5e002

Change-Id: Ic555093625358d8fc4cb1ca8c68793b5912e8ced
Merge "Methods for new "maps" property in TD Root"