Typesystem organization/refactoring

PySide2's typesystem need a refactoring because it's not too organized.

Here are a couple of things that could be improved:

• Store templates in one file (typesystem_templates.xml) which is included in each module's typesystem file.
• Standardize the way of doing things: even the simple task of increase the ref count of a certain object is being done in different ways.
• Reduce repeated code: there are many snippets that are literally the same, and we should avoid to replicate the same sections of code over and over.
• Move raw-code to templates: it's better to understand the functionality of certain methods and conversions if we avoid having a mix of raw-code and templates, so leaving everything as a template sounds like a good idea.
• Improve the current implementations/templates: the styling and way of achieving the final goal of the specific template need a little bit of love.

Hopefully this could be achieved before the release.