Implement Splash Screen handling

[GedasGa]

Platforms affected

electron

Motivation and Context

Fixes #47

Description

Allow users to place the splash screen image inside any folder. If the user defines the correct location in the config.xml, we take that image and place in the appropriate folder in the {project_root}/platfroms/electron/. As well, set the correct source in the {project_root}/platfroms/electron/config.xml file.

Testing

npm t

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[codecov-io]

Codecov Report

Merging #48 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #48   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          14     14           
  Lines         569    600   +31     
=====================================
+ Hits          569    600   +31

Impacted Files	Coverage Δ
bin/templates/cordova/lib/prepare.js	100% <100%> (ø)	⬆️

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[erisu]

LGTM