Standardize API (Merge Models and remove 'dead' code)

[ivomp]

Merge Models and remove 'dead' code

At the moment the ('Schema') models are scattered between the Domain and the Domain.Schema projects. There are also many models (and code) that are no longer used.

The idea is to merge the Domain & Domain.Schema projects and fix all the namespaces accordingly. Also to remove all the dead/unused models & code.

[ivomp]

As a start to clean-up the code we started with a proposal for new API definition. A few workshops later and many discussion between @htbmw , @thobelacs and myself.

Quite a lot of thought was given to improve the the API for both clients and the connector itself.
The main focus points for us was:

• Obviousness & Simple
  We want the API to be self-describing and understandable
• Non-ambiguous
  No property/field can be confused and is always clear what is required/meant by a field
• Lean & Clean
  We do not want to carry any un-used or unnecessary field.
• Small
  We need & want to send a small as possible payloads over the wire.

We chose this over re-usability of code and and...

Please have a look the new API proposal:
https://github.com/OpenManufacturingPlatform/iotcon-opc-ua-connector-dotnet/tree/spike/new_api/api