Add tooltips to navigation icons in Sandbox

[leahjlou]

As a new user, I have found navigation within the Sandbox page to be unclear because the menu is only icons. Tutorials & docs published by Hiro reference these sections by name, but you cannot see the name until you click on the icon to navigate to that section.

I think it would be useful to display tooltips on hover or focus of the nav icons. The tooltips would read: "Write & Deploy", "Call a Contract", "Send STX", and "STX Faucet".

Alternatively, the navigation could be changed to display the text at all times, but that would require larger UI changes to the page, and I think tooltips would be a quick improvement.