Fix #5 and add showsMyLocationButton

[omardlhz]

Fixes #5 and adds showMyLocationButton.

It converts a ReactDOM to a HTMLElement and appends it to map controls.

If we dont want to use ReactDOM, we can create an html element like here:

https://github.com/margaridafp/google-maps-current-location/blob/d6c3c5c1ec2c2d8e5165c7729ad9d02502556555/src/LocationButton.ts

Screenshot:

[teovillanueva]

Hey! Thanks for the PR. Let me know if this is ready to merge! LGTM!