fix: copy issues, compile target, trace app, add overwrite and debug option

Merges - #6
Thank you @nickofthyme

This adds the following:

• Set transpilation target to node12
• Copies the trace/ app to the final merged report only if any of the original reports contain it. All trace .zip test files were already being copied correctly.
• Adds debug option to allow user to control verbosity. (default: false)
• Adds overwriteExisting option to control overwriting existing report. (default: true)
• Fixes error with contentFolderPath when copying data/, it was not joining the src and filename path correctly. See code line diff here.