improve carbonprice/exogenous doc; allow running fixOnRef non-interactively

[orichters]

Purpose of this PR

• 45_carbonprice/exogenous requires cm_iterative_target_adj = 0 to make sense, see https://mattermost.pik-potsdam.de/rd3/pl/o4df54tps7g6jjoe6156kdqe1o. Put that into documentation and fail if not specified
• do not force interactive mode (thus slurmConfig = "direct") for fixOnRef, but allow for it if you select it as only script
• remove all non-existing realizations from settings_config.csv, and then all columns and rows that were 1 everywhere because of this.

Type of change

• [x] improve documentation, small adjustment in output script

Checklist:

• [x] My code follows the coding etiquette
• [x] I performed a self-review of my own code
• [x] I explained my changes within the PR, particularly in hard-to-understand areas
• [x] I checked that the in-code documentation is up-to-date
• [x] I did not adjust the reporting in remind2
• [x] I did not adjust forbiddenColumnNames in readCheckScenarioConfig.R
• [x] All automated model tests pass (FAIL 0 in the output of make test)
• [x] No need to update the changelog CHANGELOG.md

Run that fails on wrong settings:

/p/tmp/oliverr/remind/output/testOneRegi-exogenousfail

[orichters]

thnaks for cleaning settings_config.csv!

You misspelled "snacks"! Looking forward to it :)