Backports some fixes from 3.8 series to 3.7 series

[bsneed]

• Uses previously cached settings if unable to retrieve from server.
• Settings were being cached already, just not used.
• If no settings are present (server or cached), fallback to the barebones config.
• Fixed LIB-1698; Differences observed in how ios/android pass userId/anonId in traits.
• Pulled in fix for GCD dependency issue.

[codecov-io]

Codecov Report

Merging #867 into releases/3.7.1 will increase coverage by 0.82%.
The diff coverage is 77.77%.

@@                Coverage Diff                @@
##           releases/3.7.1    #867      +/-   ##
=================================================
+ Coverage           86.28%   87.1%   +0.82%     
=================================================
  Files                  52      52              
  Lines                2793    3002     +209     
=================================================
+ Hits                 2410    2615     +205     
- Misses                383     387       +4

[danieljackins]

🚢 LGTM