[feat] Manually add Tailwind classes to multiple elements simultaneously

[drfarrell]

Related to #173

Right now, the user cannot select multiple elements, then manually input a tailwind class in the upper right corner tailwind input box. Ideally the user is able to apply more than one class at a time to elements that are multi-selected just like they can with the property inputs below the tailwind input box.

If a user selects two elements, one without a background and another with a background, then adds-in bg-color-500, swap bg-color-500 for the background of the element that already has it, and add it to the element that doesn't have a background.

Keep in mind that this also needs to work for the prefix classes like hover:, sm:, lg:, etc.

We should probably ignore assigning classes to components this way to prevent weird behavior. So, if a user selects two non-components and a component, apply classes to the non-components but the user has to individually select the component.