Allow maximize & fullscreen in modal

[SamMousa]

When in modal mode all buttons except close are hidden. It makes sense to hide minimize (since it is a modal), however maximize and fullscreen could make perfect sense.

I propose to add a configuration for this:

buttons: {
   minimize: false,
   maximize: true,
   fullscreen: true,
   close: true
}

Setting modal to true would change the default values for buttons but explicit config would always have priority.

[gvangass]

I second this proposal