add caption selecttext when option is selected

[applizem]

When single is true, and the user selects a value, the selecttext prop is no longer displayed. The user can no longer know the name of the selectbox.
I added the props below:

• showSelectTextCaption (false by default) to show or hide caption when option is selected.
• selectTextCaption (style) to define custom style for the caption

On the other hand I also added "viewSelector" style to have the be able to stylize the view which includes the selector. I wanted to add flex: 0.5 on it but I could not.

[renrizzolo]

I would encourage you to use the renderSelectText function instead.
I will change it so you can return a component or a string, so you can style it how you need.

[github-actions]

This PR is stale because it has been open 45 days with no activity.