Add external trigger support
Allow to change triggering setting on the go
Move trigger configuration code to separate functions
Apply triggering settings only if changed
Wrap trigger code into class
Move all trigger code to single Trigger class
Rename Trigger methods for reconfigure
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).