Added Modal Component

[mathis-m]

Added modal with popup branch merged

[s-bauer]

• [ ] isClickableOutsideFocusTrap and isBlocking is redundant. It's only included in the react library due to the common interface IAccessiblePopupProps. Let's just keep isBlocking and remove the other one.
• [ ] Closing animation missing
• [ ] Unable to close popup by clicking outside of it
• [ ] Don't use function props like onDismiss. Use an event! (``$emit("dismiss")`)
• [ ] You removed containerClassName and scrollableContentClassName and therefore lost the functionality to style the inner components. That's why you need these ugly flex and center properties. Get rid of them and add back the two ...ClassName properties!
• [ ] The FocusTrapZone is missing a :class="classNames.main". Also the custom style is wrong, as the FocusTrapZone should not be 100% height and width. Compare with https://developer.microsoft.com/en-us/fabric#/components/modal
• [ ] OfficeOverlay has a "visible" property now, which you did not set, so it's always false.
• [ ] Your state property makes no sense. A state can never be a getter only! Just use normal class fields for that kind of stuff