Move to YAML for chart configuration files

[jwildfire]

Overview

Remove the charts data set and instead save chart configurations in YAML files. General workflow remains the same, with a chart configuration file passed to safetygraphicsApp()

Details

• a YAML configuration will be required for each renderer. For now, they yaml files are saved in safetyGraphics/inst/config/charts, but will very likely be migrated safetyCharts before the v2 release.
• Adding a new MakeChartConfig() helper function that will accept a list of locations where chart config YAML objects are saved.
• Several options will be added and removed from the config files. Need to add full documentation in a wiki page (and eventually in a vignette)

[jwildfire]

Added detailed documentation in the wiki: https://github.com/SafetyGraphics/safetyGraphics/wiki/Chart-Configuration-in-v2