Round notif corners on swipe

Bug: 171817112
Test: manual (lockscreen & shade)
 - swipe (first/middle/last) notif in section, corners round
   - let go, corners restore
   - with half swipe menu, corners restore when menu shows and hides

Change-Id: I9897c0a9fbfd481e72e6ad0f724761d3ace7a99d