add leading position for tags

[mwonng]

Change summary

Add a position ahead of node type name with tooltip as pictures.

What problem it solve?

Current all BlockNodeView have only position number before the type name, but it actually after node opening tag, this fix show exactly before and after position in the structure view.

// [0]<p>[1]text</p>
<p>text</p>

This will a little confuse for new Prosemirror user to identify position,

What it looks now?

[d4rkr00t]

Also I caused a bit of conflicts by removing emotion :) I'm sorry...