Make behavior of the PRESENCE_STATE 'e' option more consistent.

When writing presence state, if 'e' is specified, then the presence state will
be stored in the astdb encoded. However, consumers of presence state events or those
that query for the presence state will be given decoded information. If base64 encoding
is desired for consumers, then the information can be base64-encoded manually and the
'e' option can be omitted.

closes issue ASTERISK-23671
Reported by Mark Michelson

Review: https://reviewboard.asterisk.org/r/3482



git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@413183 f38db490-d61c-443f-a65b-d21fe96a405b