adjust NPi carbon price settings

[orichters]

Purpose of this PR

• Old setting lead to very high prices in developing prices in 2100, around 60$/t. Now, go back to 25$/t global convergence. I'm sure that underestimates a bit what might be going on in industrialized countries, but I don't want to give up on global convergence at the moment.
• I also moved the historical data to the core to avoid that any setting has no historical CO2 prices, as it may happen if you fix on a Base run until 2020, that you miss the 2010 and 2015 prices, see below.
• test runs for NPi and NDC with one single iteration are running in /p/tmp/oliverr/remind/output. With dumpgdx fulldata.gdx pm_taxCO2eq 20[0123][05], one can have a look whether that is more or less correct. Running a full scenario would not fit into today's schedule, I guess.

Type of change

• Bug fix

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
• All automated model tests pass (FAIL 0 in the output of make test)
• The changelog CHANGELOG.md has been updated correctly