Review yc.js to make sure we use best OOP practices in our JavaScript core code

TD: At the moment we have a number of custom functions in yc.js that apply to different parts of storefront. Need to modularise these functions to add meaning to their use and better understanding of api provided.

For example modular pop up is a function on context object with many options used by various modules. This functionality can be moved to context.ui.modal = {} which would have distinct simple predefined modal windows ready to use.