[Fix] Fixes #183
[Fix] Ensure there is no change in the page's scrolling position when calling selectMostSensibleCU(), even if the CU's "main element", that gets focused as a result, is outside the viewport
[Fix] Fix issue where when scrolling down we would "stuck" on a large CU
[Feature] Improved  `findFirstSensibleCUInViewport` to take the areas of partially visible CUs into account as well

Plus, minor related changes