TitleBarTab.cs - Make some properties public

[Haltroy]

Some properties (like TabImage, Area etc.) are internal, thus making an override for BaseTabRendere.Render difficult since other programs can't access those properties. This PR fixed that by making those properties public so other apps (that use EasyTabs) can edit them, thus making process of "creating your own tab renderer" easy.

Example of error:

     ...
     namepace AppThatUsesEasyTabs {      
        public class SomeNewTabRenderer : BaseTabRenderer
        {
        
                 //...

        protected override void Render(Graphics graphicsContext, TitleBarTab tab, int index, Rectangle area, Point cursor, Image tabLeftImage, Image tabCenterImage, Image tabRightImage)
                {
                    if (base._suspendRendering)
                    {
                        return;
                    }
        
        			// If we need to redraw the tab image
        			if (tab.TabImage == null) // <--- Error: tab.TabImage cannot be found.
        
        ...

[Haltroy]

I thought I should show an screenshot from VS so here it is: