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.

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.

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.

Initial commit of the new 2.x branch of Charts. Full porting to D7, new Google Charts and Highcharts support. Expanded docs and API support.