start making charts more accessible by adding in three libraries for exporting data and viewing it as a table

Enable donut option for Highcharts and Google Charts (there's still work that needs to be done to these for multiple Chart attachments). Also adds a message to the Charts API Example module if the Charts default settings have not been configured.

Fixes: 2879174 and 2879294. Also improves a bug to C3 and Google that made it so that attachments were displaying the wrong chart type.

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.

Add an example module for people wanting to understand how to use the Charts module without making use of Views. Also fixes small issue with X-axis title in Highcharts.

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.