add BECCS qtty target to regipol

[orichters]

Purpose of this PR

• expand the implicit quantity target calculation in regipol such that CCS and BECCS can be differentiated

• You can enter your target in Mt CO2 in cm_implicitQttyTarget

• Renato told me that adding too many time-steps in the switch may lead to strange behavior and bad convergence, but dragging down at both ends with values a bit below the actual goals worked very well.

• the run below is with 2060.GLO.tax.t.CCS.biomass 4300, 2080.GLO.tax.t.CCS.biomass 4300, and it nailed it quite well, I think
  

• the run below is with 2060.GLO.tax.t.CCS.biomass 3800, 2080.GLO.tax.t.CCS.biomass 3800 and that also looks very convincing.
  

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 did not adjust the reporting in remind2 as it was not necessary
• All automated model tests pass (FAIL 0 in the output of make test)

[orichters]

Implemented the change you requested, compiled and it looks good.