[ISSUE #46] Refactor and split core module

[Pil0tXia]

Fixes #46

• Split classes in core module to other modules
• Move Spring Boot dependencies to common module, because some dto/utils may need spring annotation support and packages like RestTemplate.

Further work: The implement classes need to integrate with FunctionManager. (how?)

[Pil0tXia]

@githublaohu Do we need to consider the implementation classes from the core module as service beans when referencing them? It seems better not to?

Edit: better not to.