introduce WP_CLI::colorize() utility
use Mustache templates to display plugin/theme details
refresh `core version` output

* remove manifest version (absent from recent WP releases)
* remove redundant stability label for core versions
* use Mustache template and replace tabs with spaces
use WP_CLI::colorize() in CommandWithUpgrade
move line() method from loggers back to the WP_CLI class
behat: partially delete quiet run test

output from WP_CLI::line() is no longer suppressed, since we can't be
sure it's not the essential output (think `wp core version`)
Merge pull request #517 from wp-cli/colorization

Keep color handling out of WP_CLI::line()