[Enhancement] Dialog box button and text color

[redcurry]

Summary

Provide a way to set the button background and text colors for cells that pop up a dialog box.

API Changes

For example, the PickerCell could have bindable properties ButtonBackgroundColor and ButtonTextColor to specify the button colors.

Intended Use Case

This would be mostly used in cases where the theme of the app is non-standard, such as a dark theme.