Application names are now lazily loaded

Previously when SmsApplication.getDefaultApplication was called, application
names were loaded for all candidate apps. The problem with that approach
that names are expensive to load and not always needed.

The implementation has been changed to only load application name when
it's requested by getApplicationName(Context).

Bug: 26237300
Change-Id: Ia711b7db8b979af8f7a1be7eefbce20f3e0ab1df