res_pjproject: Add ability to map pjproject log levels to Asterisk log levels

res_pjproject:  Add ability to map pjproject log levels to Asterisk log levels

Warnings and errors in the pjproject libraries are generally handled by
Asterisk.  In many cases, Asterisk wouldn't even consider them to be warnings
or errors so the messages emitted by pjproject directly are either superfluous
or misleading.  A good exampe of this are the level-0 errors pjproject emits
when it can't open a TCP/TLS socket to a client to send an OPTIONS.  We don't
consider a failure to qualify a UDP client an "ERROR", why should a TCP/TLS
client be treated any differently?

A config file for res_pjproject has bene added (pjproject.conf) and a new
log_mappings object allows mapping pjproject levels to Asterisk levels
(or nothing).  The defaults if no pjproject.conf file is found are the same
as those that were hard-coded into res_pjproject initially: 0,1 = LOG_ERROR,
2 = LOG_WARNING, 3,4,5 = LOG_DEBUG<level>

Change-Id: Iba7bb349c70397586889b8f45b8c3d6c6c8c3898