Some enhancements re config data commands on command line.

I've done a little bit of work around displaying, setting and deleting config data on the command line...

 1. Display of --config-show now in column format, rather than just using print_r:

    $ phpcs --config-show
    jsl_path:    /home/kguest/bin/jsl
    testVersion: 5.3
    $

 2. Exceptions when writing to non-writable CodeSniffer.conf caught:

    $ phpcs --config-set testVersion 5.5
    Config file /usr/share/php/data/PHP_CodeSniffer/CodeSniffer.conf is not writable
    $
    $ phpcs --config-delete jsl_path
    Config file /usr/share/php/data/PHP_CodeSniffer/CodeSniffer.conf is not writable
    $