Add permanent total to the bottom of checkout, move cart button to above total

[grablair]

Fixes #261

• Adds a line above the checkout button showing the total amount
• Moves the show/hide cart button to just above new total amount, in the center of the page, and changes the icon to chevrons

Checklist

• I have read the contributing guidelines.
• My code is of good quality and follows the coding standards of the project.
• I have tested my changes, and they work as expected.

Thank you for your contribution! 🎉

[daveearley]

Thank you for this! Apologies for the delay in reviewing. I've implemented similar changes while working on another feature and now need to find a way to incorporate both updates effectively.

[daveearley]

I very much appreciate the effort here, however, I'm going to close this PR, as similar changes have been implemented in the v1 branch.

Thanks again!