Make element visiblity check configurable

[gajus]

Adds two configurations:

• checkHorizontalElementVisibility (defaults to true) – toggles check of horizontal element visibility check.
• checkVerticalElementVisibility (defaults to true) – toggles check of vertical element visibility check.

The primary use case

• Websites that rely on horizontal navigation.
• Web components that contain animated content (using setInterval), such as the carousel.

Example use case

Website contains a carousel element. Images in the carousel are using lazy loading. Carousel transitions (loading new content) are controlled using setInterval. In such case, simply adding scroll or re-indexing the images on the page upon click event is not enough – it would require running re-indexing multiple times. A simple solution is to disable horizontal visibility check (thus the hidden content in the carousel will be loaded as soon as carousel scrolls into the view).

[gajus]

In relation to #103

[dinbror]

Hey @gajus

Sorry for the late reply. Thanks for the PR.
Normally with carousels I'm using the public ´load´ function to load what slides into the view. Wouldn't that also solve your issue?

[idoshamun]

I find this PR very useful for my use cases as well.
Sometimes I animate elements horizontal from outside the viewport to inside.
I want the images to be loaded already when animating in