The sudoers command now creates a safe wrapper script

Sudoers now creates a safe wrapper script that performs sanity checks on sudo :
* wrapper generated in /usr/local/bin (name includes version to allow multiple wrappers on the same system)
* sudoers command now generates a one-line file in /etc/sudoers.d
* SudoWrapper use the new wrapper
* Removed unused Config#validate method

Should fix #269