Only add top-borders when accounts page is sorted by date

[polltery]

Currently the top borders are added on page load and whenever any date element is added, but it's pretty useless when this happens.. I recommend we add a check so this only works when account page is sorted by date.

I did some r&d and i think this function can help check if account is sorted by date..

document.querySelector('.is-sorting').classList.contains('ynab-grid-cell-date')

Also update the date box to show (Y+) with a tooltip to let the users know the plugin is loaded and working