Clean ups in eve infrastructure and improvements in code generation

[egparedes]

List of changes:

• Fix mypy issues
• Generic implementation of Template subclasses for different template engines
• TemplatedGenerator looks for templates in the class dict (the same as methods) instead of in the internal Templates class
• Custom visit_ methods might be defined for any type, not only for Node subclasses
• Changes in dependencies versions
• Changes in pre-commit and setup.cfg config

TODO after this PR (changes made by havogt):

• re-enable mypy in pre-commit, was disabled due to an error for python 3.8 which I couldn't solve