Changes from pareview.sh, including removing unused code and fixing issues related to the implementation of ChartsInterface.

Created a ChartsInterface as a place to define constants. Also moved the API example module into the modules folder. And fixed code formatting in some places.

Responding to issue 2869541: Only display libraries that are enabled as options in the Charting Library options field.

This commit takes all sub-module-specific code out of the core charts module, making the module more extensible. It also improves the libraries.yml files and removes unused code from various parts of the site.

add default configuration form to Config page, fix the link to add a new view, and minor pareview fixes, particularly short syntax for arrays

Charts can accept 'create secondary y-axis' option from Chart Attachment displays. This commit also removes a bug in Charts Google that led to duplicate empty fields.