Galaxy Engine SPH Major Update

This major update includes many new features and changes, with the biggest new feature being SPH fluids. Now stuff like simulating planet collisions and formations are possible in Galaxy Engine.

Changelog
-Added SPH fluids simulation
-Added SPH materials
-Added SPH color visuals
-Added spaceship mode which allows to control particles
-Added spaceship gas toggle button
-Added different screen sizes support
-Added fullscreen mode
-Added selected particles color customization settings
-Added copy-paste feature
-Improved density color and density size visuals
-Made selection color brighter
-Modified particle texture to be smoother
-Galaxy Engine will open in fullscreen by default
-Changed window name to "Galaxy Engine"
-Separated physics and visuals sliders
-Slightly modified default colors
-Removed pairwise gravity simulation
-Removed Barnes-Hut button (the only available gravity algorithm now is Barnes-Hut)

Known issues:
-There are some minor instabilities in SPH mode
-Currently, the SPH physics are not incompressible
-Clumped particles in Collisions mode still spin. Collisions mode might be removed