Fix/36-multiple-children-objects

[pogi7]

Checklist before submitting a merge request

• [x] I have reviewed CONTRIBUTING.md document
• [x] All commits have been signed-off for the Developer Certificate of Origin. See here.
• [x] I have added my contribution to CHANGELOG.md
• [x] I have documented my code in the OML Vision Docs

Description of contribution

Fix bug with generated a view with 2 sets of layout objects that contain the 'children' attribute

closes https://github.com/opencaesar/oml-vision/issues/36

Testing performed

• [x] I have added unit tests to cover additional functionality

How to Test Expected functionality changes

OML Model:

1. You can use this OML model for testing https://github.com/pogi7/kepler16b-example
2. Update the src/vision/pages.json file to look like this. PLEASE DON'T COMMIT/PUSH THIS CHANGE.:

   [
   { "title": "Home", "path": "/", "type": "home" },
   {
   "title": "Kepler16b",
   "type": "group",
   "iconUrl": "https://nasa-jpl.github.io/stellar/icons/satellite.svg",
   "children": [
     { 
       "title": "Objectives",
       "type": "table",
       "path": "objectives"
     },
     {
       "title": "Missions",
       "type": "tree",
       "path": "missions"
     },
     {
       "title": "Components",
       "type": "diagram",
       "path": "components"
     }
   ]
   },
   {
   "title": "Test",
   "type": "group",
   "iconUrl": "https://nasa-jpl.github.io/stellar/icons/satellite.svg",
   "children": [
     {
       "title": "Requirements",
       "type": "tree",
       "path": "requirements"
     },
     {
       "title": "Connections",
       "type": "table",
       "path": "connections"
     }
   ]
   }
   ]

3. Click the OML Vision eye icon
4. Verify that all views can open when clicking them in the Home page or in sidebar

Additional context