Refactoring for cmake build settings

- Moved additional header files to /src
- Simplified header-paths
- Added missing license title for getopt
- Added comments and sections to CMakeLists
- Improved file structure (partially)
- Co-build st-util with st-info & st-flash
- GUI: Renamed .ui file to match executable
- Added install targets for executables
- Added missing "uninstall" cmd to Makefile