Added customizable img filters

[Sepitus-exe]

So far I decided to implement only 4 variables. The rest of the filters seemed universal enough as to be left static. There are however few things to mention.

The extra study variable is shared between the extra study image itself and some similar more obscure images as seen below.

The filter of box-overlay images/buttons might be too obscure to warrant inclusion.

[Sepitus-exe]

I will close the pull request for now as the implementation was lacking