Logger activity should be able to be redirected

[ayh20]

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[X] enhancement request
[] feature request
[] support request
[] general question

Current behavior (how does the issue manifest):
Logger outputs to STDIO
Expected behavior:
It should be possible to tell a Flogo app where to direct the log output.
Minimal steps to reproduce the problem (not required if feature enhancement):

What is the motivation / use case for changing the behavior?
As Flogo apps are deployed to more diverse environments we need more control over where the log data goes to. We should be able to do things like direct the OP to a file, or a central logger app (for example)
Please tell us about your environment (Operating system, docker version, browser & verison if webui, etc):

Flogo version (CLI & contrib/lib. If unknown, leave empty or state unknown): 0.X.X

Additional information you deem important (e.g. issue happens only occasionally):