New CSS component: Button

[devmount]

Is your component request related to a problem? Please describe.
Buttons are already supported by core styles. However, it would be nice to have some additional styling for further use cases than just triggering an action on click and providing those styles as a class to apply them to different elements like links too.

Describe the component you'd like for that problem

• Introducing a new class .button
• Providing a secondary button, e.g. with a .hollow class
• Providing a positive/negative colored button
• Providing a busy state for a button, containing an indicator, e.g. with a .busy class
• Providing a ghost button, making a button element look like a normal link
• Introducing a new class .button-group for the parent element, to make multiple buttons appear as a single, segmented button.
• Making buttons work with utility class rounded-full
• Making the button class work on link elements too