Dynamic loading examples

[liqul]

1. support dynamically loading examples for different roles
2. move loading example to role base class
3. rename codeinterpreter_examples to code_generator_examples in project folder; need manual migration

[Jack-Q]

Seems most of changes are the same as experiences loading, maybe it would work in the same way. Not sure whether would need to have a common class to abstract these shared loading logics together in the future.

[liqul]

Seems most of changes are the same as experiences loading, maybe it would work in the same way. Not sure whether would need to have a common class to abstract these shared loading logics together in the future.

Exactly, that is why I left a todo item in the comments. They all belong to a category that should be dynamically loaded in runtime. A third could be the plugins. But I'm not sure how to abstract at this moment.