Unify namespaces

[Sevitas]

Motivation

Unify namespaces:

• some entities have namespace matching their full project structure
• some entities match just project's namespace

Proposed solution

Unify namespaces throughout the whole solution structure/match the project namespace in all classes

[Sevitas]

I've checked projects:

• Kentico.Kontent.Delivery.Rx.Tests -> no need to change anything
• Kentico.Kontent.Delivery.Rx -> no need to change anything
• Kentico.Kontent.Delivery.Tests -> no need to change anything
• Kentico.Kontent.Delivery -> no need to change anything
• Kentico.Kontent.ImageTransformation.Tests -> namespaces fixed in https://github.com/Kentico/kontent-delivery-sdk-net/pull/288
• Kentico.Kontent.ImageTransformation -> namespaces fixed in https://github.com/Kentico/kontent-delivery-sdk-net/pull/288

the other half will be checked and fixed by @MiroKentico