Fix call duration talkback verbalization.

+ Uncomment code which generates content description.
+ Pass in local context, rather than System context, for getting
the plurals resource strings. This fixes a crash happening in
languages even if correctly translations existed.
+ Catch Resource.NotFoundExceptions in the utility which generates
this human-readable string so that for locales missing the
translation we don't crash the whole Dialer.

Bug: 20813003
Change-Id: I861078a116d2d31f3ac361757a14581726a78f1c