Add category paging support for Large Category list

[aribronstein]

It seems like when you have a large list of categories (we have 992) the Magento backend stops responding because it has to many connections at once from the same client.

Any easy way to batch the categories into smaller chunks just like the products?

[pkarw]

Hi! I think we should implement the paging feature exactly as it’s done in the products

The adapter to be changed is: https://github.com/DivanteLtd/mage2vuestorefront/blob/master/src/adapters/magento/category.js

If You could take care of this and publish as a PR - that would be great!