Add process tagging for scheduler process

On a server hosting multiple apps and multiple instances of
resque-scheduler, it can be difficult to tell which scheduler
goes with which app. This change adds an APP_NAME environment
variable that, if set, appends the app name to the procline.
Merge branch 'process-labeling' of https://github.com/nmeans/resque-scheduler into nmeans-process-labeling

Conflicts:
	lib/resque_scheduler/tasks.rb
Making Resque::Scheduler.app_name work like other settings
Merge pull request #308 from meatballhat/merging-nmeans-process-labeling

Add process tagging for scheduler process