[feat] Make the "Enter" key work on a modal to advance it to the next step.

[drfarrell]

For all of the keyboard warriors out there – make it so that hitting "Enter" on a modal will submit the modal. #753 partially seeks to solve this problem and could be a reference.

Bonus:

• Make the "Delete" key work on the "delete element" modal as well as the enter key
• Let the user "tab" between the button options and then hit "Enter" to advance.