[Custom Header] Fix customHeader validation

Instead of just replacing all of header, keep close button rendered!

Watch that the close button disappeared

Now, we have the button plus the custom header setted

[Feature] Custom icon and prop elements to message

Hello guys, finally it works! ✨✨

As this is my fist library, i did encountered some bundle errors, and studied a lot trying to fix it.

And now that (thank God, works) I'll start working on new features:

• Add props that will allow you to customize header
• Add props that will allow you to pass React components through message, instead of just strings (as it is now)
• Add animation, as slide and timer! (As default)
• Ajust some alignments from components

If you like more features, please add on Issues or comments 😁😁