Preparatory work to move Telecom to system service.

- Removed use of TelecomApp.getInstance() as context.
- Refactored singleton logic and initialization to support being
performed from a SystemService.
- Note: You will see some commented out references to
"import com.android.internal.R"; these must uncommented when the code
is moved to a system service.
- You will also notice in PhoneAccountRegistrar.java a comment block with:
"UNCOMMENT_FOR_MOVE_TO_SYSTEM_SERVICE"
The code in that comment block will replace the existing file path
code.
These were added as a convenience so that I can run a simple sed script
to make the required changes to the code in an automated manner once it
is moved to its new location.

Bug: 17364651
Change-Id: I8e80e9cffc481b688c10a2bca0b59f5ccf8e0fb2