Strip comments from compiled PHP (artisan optimize)

The argument added strips out all of the comments, reducing the size of the compiled PHP file to half.

This should likely improve performance but I haven't tested it. 

Note that the PreCompileCommand has two more options that we are not using: 

            ->addOption('fix_dir', null, InputOption::VALUE_REQUIRED, 'Convert __DIR__ constants to the original directory of a file', 1)
            ->addOption('fix_file', null, InputOption::VALUE_REQUIRED, 'Convert __FILE__ constants to the original path of a file', 1)

These have not been enabled here though. Someone else should probably decide on that.

Also, if there is a big difference in performance, doing a "php -w" to strip the whitespaces afterwards as well might be a good idea.