UI System Improvements

[KilledByAPixel]

The first pass of the UI system is finished and implemented everywhere.

Demo of just the UI System

Next steps are to improve the system...

• A container class that can display items in a grid layout
• Improve ability to auto position objects relative to screen (top, bottom, left, right, center)
• Improved text entry functionality

What would you like to see? Add your UI feature requests below.

[brandongregoryscott]

• Ability to render a grid w/ gap between items (sounds covered by bullet point 1)
• Flex positioning or something similar, so it's easy to implement a header component like this (might be covered by bullet point 2)

• Ability to set width/height relative to a parent (i.e. 50%)

Another piece of feedback is potentially renaming the UIScrollbar to UISlider. Not sure how you feel about breaking changes, but IMO Scrollbar is a poor name for this class. I would expect that to be something used for scrollable content in a container (which I would also like to see implemented somehow! Though I think that's essentially asking for "windowing" to render some subset of content based on the visible area of a container)