Make this thing readable by wasting a couple of bytes for spaces and newlines.

As an added bonus, save some stack space by making usage_string a static const.
Signed-off-by: Stefan Knoblich <s.knoblich@axsentis.de>

make sure dtmfinband gets initialized.
make gk-identifier and gk-interface settings optional (documentation sayed that about gk-identifier already)

FS-3307 --resolve thanks, in the future, be sure to not include vanity comments.  The intention of the patch will be preserved by the jira ticket.  Also check our code formating guidelines.  Some of the patch was redundant so it was removed, mprintf already asserts when it doesn't work, and execute_sql_now both frees the sql string and locks the mutex for you.

add prefix chars to playback_terminators + means include the term in the string and x means include the char and return SWITCH_STATUS_RESTART eg #+* only includes the * if you type it but not the #