Title (tooltip) missing for GeoBookmark button

[labronico0586]

It is not possible to set a title (tooltip) for the button used to activate the geo bookmark button, as in other controls, using options.title in constructor.

A possible workaround is to set title accessing the internal button, but this ties the user code to the internal implementation and should be avoided.

[Viglino]

👍 I've added the option.