Support template header and footer

[egyedia]

Old editor:

CEE:

Template section:

  "_ui": {
    "pages": [],
    "order": [
      "Text field"
    ],
    "propertyLabels": {
      "Text field": "Text field"
    },
    "propertyDescriptions": {
      "Text field": "Help Text"
    },
    "header": "Template header",
    "footer": "Template footer"
  },