Fix icon flicker from home-> overview when 3 button navigation is enabled in 3P launcher.

Flicker occurs due to calling fade for 0 to 1 twice which needed to be corrected.

Also renamed confusing terms for updating alpha of app icons.

Test: Manual. Install 3P launcher, 3 button navigation enabled, go to Overview.
Fix: 378419654
Flag: EXEMPT bug fix.
Change-Id: I46ff564712f5fd217c5992042ee441242159fe99