Add new apps

We have added info for the following new apps.
- A Boltzmann transport equation solver for calculating lattice thermal conductivity based on phonon information obtained from first-principles calculations, “ShengBTE“
- A software package for calculating lattice thermal conductivity based on phonon information obtained from first-principles calculations, including four-phonon scattering processes, “FourPhonon”
- A Python package for extracting structural features from point cloud and image data using the mathematical framework of persistent homology, “homcloud“