Allow for enabling quote trimming via a system property

[triceo]

The property is picocli.trimQuotes.

When set to true or when left empty, quote trimming will be enabled by default. Otherwise, the default is false. Regardless of the value of the property, the value can still be overriden through the usual API - therefore there is no break in backwards compatibility.

[codecov-io]

Codecov Report

Merging #562 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #562      +/-   ##
============================================
+ Coverage     89.13%   89.14%   +<.01%     
  Complexity      286      286              
============================================
  Files             4        4              
  Lines          3967     3970       +3     
  Branches        976      977       +1     
============================================
+ Hits           3536     3539       +3     
  Misses          212      212              
  Partials        219      219

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/picocli/CommandLine.java	89.18% <100%> (ø)	161 <0> (ø)	⬇️

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[remkop]

Merged. Thanks for the PR!