Use DefaultDialerCache in Telecom (part 2)

Use the DefaultDialerCache throughout Telecom whereever the value of the
default dialer for a particular user is accessed or modified. Also moves
the DefaultDialerManagerAdapter to DefaultDialerCache since
TelecomServiceImpl no longer directly uses it.

Test: Unit tests and manual tests as specified in design
Change-Id: I5d8f46b4a236e570528425b4010976ac837644ac