[#69] Additively blend particles and make them look rounded

include/vkcv/PipelineConfig.hpp

projects/particle_simulation/shaders/frag_space.spv

projects/particle_simulation/shaders/frag_water.spv

projects/particle_simulation/shaders/particleShading.inc

projects/particle_simulation/shaders/shader.vert

projects/particle_simulation/shaders/shader_space.frag

projects/particle_simulation/shaders/shader_water.frag

projects/particle_simulation/shaders/vert.spv

projects/particle_simulation/src/main.cpp

src/vkcv/PipelineManager.cpp