Rename PAFlowProcessor to PALogProcessor
Fix no samples being taken when the sample rate is 1/1
update to receive THREAT and TRAFFIC logs from PA

Generalizes PALogProcessor to receive column lists, file name at
instantiation. run.rb pulls the configurations from samples.yaml then
instantiates/configures the required objects.
Don't write the CSV header if the file already exists

Fixes a case where the logger is restarted and a CSV header is appened
to a CSV file that already has a header
Add cheap threading so threats don't block traffic