NEW: Added component question type

[venarius]

Hey, again 👋

This is also something we need: A question type where we can show our own components (e.g. contact forms). This PR adds such component and I also added a seperate example for it where you can test it out.

It currently adds two props to the question model:

• component -> Here the user needs to supply their component.
• validateComponent -> If set to true "vue-flow-form" will call the isValid() method on the given component to check if its valid before it continues.

If you have any questions or feedback, just let me know 😀

[phre1]

This is a really interesting suggestion - although we feel this should be tested and refined a bit more. If we decide to support this, we'd need to create and document some sort of plugin API that custom components would need to follow to make them fully integrated with the rest of Flow Form. We'll pull this request into an experimental branch so we can further test it out and possibly improve it.