v0.1-alpha.3

CSG v0.1-alpha.3

What's new:

• Different colored bonds with varying thicknesses for different bond orders.
• A legend to convey information about the different colors used.
• The chemical structure window now shows the chemical formula and its geometry in its title.
  
• The chemical structure window respects the dark/light theme setting.
  
  
• UI tweaks.
• Bug fixes.