Add setlocal to prevent unintended chdir and crazy build up of environment variables
Several installer-related changes

- Build all executables to INVICTUS_ROOT/bin, not just Keyhotee
- Add an install target to copy all required files to
  INVICTUS_ROOT/install (some required files are still missing from
  bin and must be copied there manually).  Works on windows,
  will still be missing stuff on other platforms.
- Add a package target to build .zip and installers for windows
- Add an Windows icon