* Refactor notebook render
1. Merge template files and remove unused files.
2. Move render function to environment class
3. Extract notebook test cases to a new module
* Refactor chart render
1. Add render_* to EchartsEnvironment class
2. Remove engine.render
3. Remove unused template files
* Fix online between test cases.
* Update document and changelog
* Rename some functions
* Update some mistakes
* Remove debug code
* Refactor env.render_chart_to_notebook method