General Improvements: Add support for multiple button style variants to the button component

In the [design system](https://www.figma.com/file/1gbapWYZva4fCBEnPhs7FF/DockYard-Admin---Design?node-id=146%3A465&mode=dev) we have several variations of buttons, so I'd like to add support for these variants without needing to create a new component but modifying the existing component to render different styles based on the button type.

There are many places in the recent updates to the admin where we have large blue (primary) buttons where a more discreet secondary or tertiary button would be more fitting, since its not a primary action.

Also include support for an accessible icon-only button.