KAZOO-2560 - CAMP-ON feature

Look in whistle-1.0.0/include/wh_types.hrl; we have a bunch of time-related macros, like ?SECONDS_IN_MINUTE or ?MILLISECONDS_IN_HOUR to make these timeout declarations easier to read and infer the units of.

In this case, 15*60 doesn't make a lot of sense...15 minutes (60 seconds/minute * 15 minutes) or 15 hours (60 minutes/hour * 15 hours)...

`15 * ?SECONDS_IN_MINUTE` let me know right away the units are seconds, and its 15 minutes worth of them.