apps/app_sms: Add an option to prevent SMS content from being logged

In some countries, privacy laws specify that SMS content cannot be saved by a
provider. This patch adds a new option to the SMS application, 'n', which
prevents the SMS content from being written to the SMS log.

ASTERISK-22591 #close
Reported by: Jan Juergens
patches:
  DisableSmsContentLoggingByParam.patch uploaded by Jan Juergens (License 6538)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@432947 65c4cc65-6c06-0410-ace0-fbb531ad65f3