Allow hardware overflow key to be show by default.

Currently this is controlled by a system setting, but there is no way to
set a default value for the system setting. This is very useful to have
for devices that have no hardware menu key.

Change-Id: I94212def19d3e2224d79d3a89e1e2d3b2883da21
Merge "Allow hardware overflow key to be show by default." into cm-10.1