Change build system to cmake
Import the cmake build system from VTM
- move source files to lib/app folders
- no library build yet, just include files from lib/common into lencod/ldecod (as in old build)
- remove old (partly broken) build environments
- add cmake environment
- various build fixes for recent compilers (gcc 7, clang, VS 2017)
ToDo: Update build instructions in Readme
Edited by Karsten Suehring