Additional Classes/IDs for Global Theme Style

## Prerequisites

- [ X ] I have searched for similar features requests in both open and closed tickets and cannot find a duplicate.
- [ X ] The feature is still missing in the latest stable version of Elementor ( Elementor Pro. )

**What problem is your feature request going to solve? Please describe.**
I realise the Global Style settings help to create a touch-one-touch-all effect, however for other third-party plugins, such as WooCommerce in my case, I find myself constantly having to re-code the whole button style in a separate stylesheet that I then have to load above all the rest.

**Describe the solution you'd like**
I feel like it would be a great addition to have a box below the Buttons and Form Fields Theme Styles where I can simply input a class or ID that the theme style would also affect. (Each line would represent one class/ID) This would make for a TRUE global theme style feel.

**Describe alternatives you've considered**
Besides using a separately coded stylesheet each time, and replicating the same theme style, I dont see another fix....unless you add support for every plugin in the world? haha!

**Additional context**
Please see screenshot for a quick edit of what it may look like and how it may function.