APN: update/add a few apns

add Virgin Mobile USA apn

Change-Id: Ia016e19b14a173746fddbc5319fac98ca9f188c5
added Boost, Credo & Ting APNs

Also changed name of Sprint MMS apn to be clearer.

Change-Id: Iba70c5882d0c65bc25ebfbf25018739eb800d160

Conflicts:
	prebuilt/etc/apns-conf.xml
Remove duplicate Vodafone APN, correct Tele2 APN

Duplicate Vodafone entry had incorrect trailing spaces in APN and user
field
Tele2 MMS entry had an extra space in apn field.

Change-Id: I6f0c9e8d5ca9a4c197a12d92588f800d28b94338