add VEP process management

[sheridancbio]

- SystemProcessManager class now provides process management services for VEP
    - uses UNIXProcess (if available) for determining a Process pid
    - uses UNIXProcess (if available) for reaping zombies (via waitForProcessExit())
    - determines availability of ps and kill commands on local system
    - manages processes launched if needed tools are available
    - starts ReaperDaemonThread when first VEP process is launched
    - reaper will periodically check for orphaned child processes of a destroyed VEP process and kill them
    - reaper will periodically check for zombie processes and reap them
- unix 'ps' command output parsing encapsulated in ProcessSurveyor class
- remove thread interruption in VepRunner - now StreamTransferrer threads will exit naturally when orphaned children are killed
- shut down reaper as application shuts down

[sheridancbio]

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