add readcoupledgdx.R script to show scalars for all coupled runs, add it to tutorial

[orichters]

Purpose of this PR

• add readcoupledgdx.R script to show scalars for all coupled runs, add it to tutorial
• turn stop in checkProjectSummations.R into warning, no need to fail here.

Type of change

• New feature

Checklist:

• My code follows the coding etiquette
• I performed a self-review of my own code
• I explained my changes within the PR, particularly in hard-to-understand areas
• I checked that the in-code documentation is up-to-date
• I adjusted the reporting in remind2 where it was needed
• I adjusted forbiddenColumnNames in readCheckScenarioConfig.R in case the PR leads to deprecated switches
• I checked the log.txt file of my runs for newly introduced summation, fixing or variable name errors
• All automated model tests pass, executed after my final commit (FAIL 0 in the output of make test)
• The changelog CHANGELOG.md has been updated correctly