src: Render using a separate thread

* Move the OGL Context and render on a separate thread
* Move core rendering code to CoreRenderer class
* Use CoreRenderer in QmlRenderer to render

cli: Account for structural changes made in src

* Make changes to accomodate changes made to src for threading
* Temporarily allow only filename to be the changeable attribute from the user

test: Account for structural changes made in src

* Make changes to accomodate changes made in src for threading