Fix WP_CLI::colorize warnings

Passing an array to colorize causes warnings since the passed in value ends up being passed
into md5

Warning was
PHP Warning:  md5() expects parameter 1 to be string, array given in git/wp-cli/vendor/wp-cli/php-cli-tools/lib/cli/Colors.php on line 118
Merge pull request #1356 from jeichorn/colorize_warnings

Fix WP_CLI::colorize warnings
Example: Update one option against multiple sites

See #1367
test coverage for `wp scaffold _s`
fix `wp scaffold _s`
Merge pull request #1373 from rodrigoprimo/fix-scaffold-_s

Fix silent error for wp scaffold _s
Denote all available fields for `wp comment list`
Denote available fields for `wp cron schedule list`
Denote available fields for `wp menu list`
Denote relevant available fields for `wp menu item list`
Fix display of menu item classes in list table
Denote available fields for `wp menu location list`
Denote available fields for `wp plugin list`
Denote available fields for `wp theme list`
Formatting
Denote available fields for `wp post list`
Denote available fields for `wp role list`
Denote available fields for `wp sidebar list`
Denote available fields for `wp site list
Denote available fields for `wp term list`