[TIMOB-15193] (3_1_X) Support backgroundColor=transparent on ListView (iOS7)

Backport of PR #4701

Solution is slightly different because of different code bases.

Fixes [TIMOB-15193](https://jira.appcelerator.org/browse/TIMOB-15193)

For regression test KS and make sure default behavior is unchanged for background color. See TIMOB-15192. Run on iOS6 and iOS7