[FEATURE] sap.ui.model.json.JSONListBinding: iterate over maps

Enhance JSONListBinding to iterate over maps (by key), not just over
arrays (by index).

See http://veui5infra.dhcp.wdf.sap.corp:8080/snippix/#87920 by Malte
Wedel

PS1: PP with KTH
PS2: rebased to avoid Carousel

Change-Id: Ia6febfcea797275fb56e2eac7cdfea94e486e001
JIRA: FLPUISERVICES2014-1112
Merge "[FEATURE] sap.ui.model.json.JSONListBinding: iterate over maps"