#3463307: Slider range created for zoom controls

Closes #3463307

1. Introduced significantly smoother zoom when using trackpad or mousewheel
2. Added slider to control zoom level
3. Zooming to specific/exact values is achievable with a select menu
4. Added "debug" value to app config that will show the old "scroll iframe into view button
5. Fixed bug where pinch/mousewheel zooming while hovering the iframe didn't work
6. Reduced test flake around iframe content being initialised
7. Introduced cy.session()
8. Added new cy.loadURLandWaitForXBLoaded() command to centralise common code/reduce test boilerplate
9. Added Cypress Iframe library
10. Added tests for the Zoom.

Thanks @Gauravmahlawat for his contribution to this MR.