C/C++, Scala, git, Perforce layers, package cleaning, fixes and tweaks

• Move C/C++ and CMake packages/configuration to c-c++ layer
• Move Scala, ENSIME and sbt-mode packages to scala layer
• Move Magit and a bunch of packages to git layer
• Move Perforce p4 package to perforce layer
• Move CoffeeScript package to javascript layer
• Move ghc package to haskell layer
• Move hy package to python layer
• Remove csharp package from spacemacs layer (omnisharp anyone ?)
• Remove puppet-mode and wand packages from spacemacs layer
• Add documentation about font and a FAQ entry about ugly spacemacs banner
• Fix dospacemacs-persistent-server (thanks to quanganhdo)
• Fix C-u to scroll-up