User interface interactions

[TheAzack9]

Implement some user interface elements

• Button
• Slider
• Labels

[luringens]

Basic implementation of a button that interacts with global state has been complete. Rendering text is still an important missing feature however.

[luringens]

Currently working on text rendering.

[luringens]

Text rendering has been postponed. @TheAzack9 has made an abstraction for rendering primitives. I'm working on implementing a slider.

[luringens]

Slider implemented in e3b8436.