Refactor template includes

[koczkatamas]

Resolve the following issues:

• template includes only collected after template generation happens, so it needs to be split into a two stage process: generate code first, then generate includes
• testGenerator.includes does not work (e.g. C++)
• conditional includes should be introduced (e.g. in C++'s getType conditionally uses one:: namespace which requires OneLang.Core) - with e.g. a non-returning template action {{ includes("something") }}