Add integration with piamPlotComparison for compareScenarios

[fbenke-pik]

This PR moves the generic logic to create a compareScenarios pdf to the library piamPlotComparison.

The following files are no longer needed:

• R/compareScenarios_EDGET.R (moved to piamPlotComparison)
• inst/Rmd/compareScenarios_Transport/csEDGET_main.Rmd (moved to piamPlotComparison, EDGE-T specific code was moved to inst/compareScenarios/preprocessing.R)
• inst/Rmd/compareScenarios_Transport/cs2_latex_template.tex and inst/Rmd/compareScenarios_Transport/cs_pdf_header_include.tex (moved to piamPlotComparison)
• inst/Rmd/compareScenarios_Transport/cs2_plot_functions.R (some functions were deleted as they were no longer used, others were moved to the notebook where they are used or to the inst/compareScenarios/preprocessing.R )

The section markdowns used to generate the current pdf are EDGE-T specific and remain in this repo. To work with the new framework, they were moved to the folder /inst/compareScenarios/ and renamed to cs_NN_TEXT.Rmd (e.g. inst/Rmd/compareScenarios_Transport/csEDGET_01_energy_demand.Rmd -> inst/compareScenarios/cs_01_energy_demand.Rmd).

inst/compareScenarios/cs_06_costs_and_shareweight_trends.Rmd was refactored to use dplyr instead of data.table. The output generated has not changed through this refactoring.

Rmd files not used in the current cs2 plotting were left in the original folder inst/Rmd/compareScenarios_Transport/. If they are no longer needed, they should be deleted.

[fbenke-pik]

Closed in favour of https://github.com/pik-piam/reporttransport/pull/19