Merge pull request #9 from bgromov/trigger

External triggering support
add change log for coming 1.9.5 release
create test node that sends S/W trigger to first camera at two Hz
add S/W trigger unit test for driver node (not working yet)
set ~external_trigger in addition to ~software_trigger, so unit test works
add nodelet version of trigger test
remove unnecessary trigger parameter
only run Trigger class when camera supports that mode (#12)

Change return value from Trigger::initialize() and Trigger::reconfigure() to match comments and
to be consistent with Feature::initialize().
Fix egregious bug in hasTrigger(), thanks to Brice Rebsamen. Fixes #16
reduce unit test durations
trigger_node: log fatal error when camera does not support triggering
Make sure power is on before setting a feature to any other mode (#15).
Return corrected parameter value to dynamic_reconfigure