Make application PID file location configurable from Environment propert...

Make application PID file location configurable

The ApplicationPidListener class can now be configured to search the Environment for the occurrence of the property 'spring.application.pid-file' in order to configure the location of the PID file from the central applications configuration file. Sticks to defaults if the property is not found.

Fixes gh-1579
Okay understood. That is no problem. I just wanted not to have the end user choose the appropriate event class. The problem here is that there is no smart opportunity to decide if the event provides the `Environment`. Even only `ApplicationEnvironmentPreparedEvent` has a direct getter on it. Also `ApplicationFailedEvent` does not make sense at all. I´ll think over a smart way to do this and modify the pull request accordingly.