fix css, add parameter position, set default icon

[gpibarra]

When using the geolocate method, the geolocateLabel did not load the button's css correctly.

If the label is empty, add the button with a default icon (svg).

Also, add the Position parameter to define where on the map the new button is added.

[cheesegrits]

@gpibarra hey, sorry about the slow response, I've had some serious medical issues this year that prevented me from working on this.

Could you update the README to document your changes, including a link to the relevant Google Maps doc page with the available button positions. Then I'll merge this.

[gpibarra]

Hi @cheesegrits, sorry for my English, in the commit e5d29d4 I had already modified the documentation, do you want me to give more details?