Support for optional counter types for ordered list

[jscastanos]

The current version has a fixed list of counter types, which are the default options for ordered list.

So this PR allows an optional way to specify a list on what counter types should be visible.

Example

 tools: {
        List: {
          class: List,
          config: {
             counterTypes: ['numeric', 'upper-roman']
          }
        },
      },

Closes #128

[e11sy]

it seems, that user could specify empty array (or array with one value) for counterTypes, then Counter type option should not be displayed in tool settings (since it would never be a choice)

you can add this changes and then it would be ready to merge, thanks for contributing!