Design & implement infrastructure for calling remote smart contracts

[Robbepop]

Currently there is only an extremely bare metal and unsafe way of calling remote smart contracts.
People will basically not use this feature without support that comes out of the box from pdsl_lang or layers below.

First we need to find the perfect layer to support calling remote contracts.

• The core layer could provide some utilities to build up call-data but the user still has to provide all the necessary information about the API of the remote smart contract.

• The model layer could provide further safety features to implement automatic flushing of the contract state before calling a remote smart contract since that could possible lead to storage mutation and thus re-entrancy attacks.

• The lang layer could provide automatic API generation in form of JSON files and could also be fed by API files of dependent on smart contracts to make calling remote smart contracts nearly as simple as calling just another internal function.

[Robbepop]

Superseeded by #81