Add more config options to cat.py

[pnuu]

This PR adds the following config file options for cat.py:

• publish_port - port number where messages are published. Optional, defaults to random port.
• subscriber_nameserver - connect subscriber to this nameserver. Optional, defaults to localhost.
• subscriber_addresses - connect directly to listed servers and ports. Optional, not used by default.

[codecov[bot]]

Codecov Report

Merging #57 into master will increase coverage by 56.15%. The diff coverage is n/a.

@@             Coverage Diff             @@
##           master      #57       +/-   ##
===========================================
+ Coverage    7.72%   63.88%   +56.15%     
===========================================
  Files          18       14        -4     
  Lines        3222     2082     -1140     
===========================================
+ Hits          249     1330     +1081     
+ Misses       2973      752     -2221     

Impacted Files	Coverage Δ
setup.py	0.00% <0.00%> (ø)
pytroll_collectors/global_mosaic.py
pytroll_collectors/tests/test_global_mosaic.py
pytroll_collectors/image_scaler.py
pytroll_collectors/tests/test_image_scaler.py
pytroll_collectors/tests/__init__.py	40.00% <0.00%> (+15.00%)	:arrow_up:
pytroll_collectors/helper_functions.py	66.35% <0.00%> (+50.46%)	:arrow_up:
pytroll_collectors/scisys.py	62.18% <0.00%> (+50.93%)	:arrow_up:
pytroll_collectors/tests/test_trigger.py	92.18% <0.00%> (+57.18%)	:arrow_up:
pytroll_collectors/trigger.py	61.72% <0.00%> (+61.72%)	:arrow_up:
... and 4 more

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