Support tight lists

[d3m1d0v]

Description

In markdown-it lists rendered differently depending on the indentation between the list items (look at the distance between the elements):

Markup	Result

But wysiwyg editor always convert all lists to non-tight lists (lists with bigger distance between the elements)

Proposal

Let's preserve indentation between the list items and fully support tight lists

[makhnatkin]

We want to solve this problem by setting styles in YFM for the paragraph inside the list, so that it is displayed compactly.