Add --dry-run option to launchpad start

[gcotelli]

• Add --dry-run option to launchpad start
• Improve LaunchpadTest to make it easier to test the configuration of an application
• Improve LaunchpadCommandLine handler so it's easier to activate it by hand

Based on #64 made by @macta

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.79%. Comparing base (5bab6ee) to head (ecdc1b4).

Additional details and impacted files

@@                 Coverage Diff                 @@
##           release-candidate      #69    +/-   ##
===================================================
  Coverage              99.78%   99.79%            
===================================================
  Files                     58       62     +4     
  Lines                   3751     3870   +119     
===================================================
+ Hits                    3743     3862   +119     
  Misses                     8        8            

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[macta]

Its a bit hard to review as there are lots of format changes from symbol to string - but I like the dry-run tests, and I can see there is an option to get at config symbolically.