Paul McCartney is a songwriter driven by a powerfully playful muse, especially on his less-celebrated songs. While “Soily” and “Cut Me Some Slack” prove he's always been a rocker at heart, he remains blessed with the ability to create limpid romances such as “Bluebird” and still throw himself into quirky delights such as “Ballroom Dancing” and the electro-funk of “Temporary Secretary.”