Refactor(tabulation) Keydowns and style refactor

[e11sy]

This PR is related to the #75 issue This PR is a part of global work on List 2.0

Problems

• Nesting is not customizable
• Can not increase nesting more than 1 time

  1
  1.1.1

  is currently unavailable

• Can't customize ordered list (custom numeration or starting with custom number)

  Solutions

• Now data model meta field will contain level variable

  meta: 
  {
  checked?: boolean,
  level: number,  
  }

• Refactor rendering part Now we will have flat structure of the list, but all item will have level attribute

  <ol class="list">
  <li class="cdx-list__item" level="1" style="--level: 1">Item Level 1</li>
  <li class="cdx-list__item" level="2" style="--level: 2">Item Level 2</li>
  <li class="cdx-list__item" level="1" style="--level: 1">Item Level 1</li>
  <li class="cdx-list__item" level="2" style="--level: 2">Item Level 2</li>
  <li class="cdx-list__item" level="3" style="--level: 3">Item Level 3</li>
  <li class="cdx-list__item" level="4" style="--level: 4">Item Level 4</li>
  </ol>

• Nesting customization by maxLevel config option
• Add support for <ol> attributes in config (such as type, start, reversed)

  Status

• [x] Support new data model
• [ ] Refactor keydowns befaviour
• [ ] Support counters for ordered list in new format
• [ ] Add nesting customization
• [ ] Add ordered list customization for #66
• [ ] Refactor paste config
• [ ] Export all available lists into toolbox for #70
• [ ] List splitting for #30