Reintroduce Worker implementation for encointer

[clangenb]

#89 fixed the worker implementation for recent integritee-workers in general, but the encointer implementation is still not complete and is dangling in a state in between. To make the encointer-worker work, we need:

• Make some functions needed in sending TrustedGetters and TrustedCalls more generic, such that we can create encointer types instead of integritee types depending on the contexts (currently only integritee types supported).
• Probably update the type definitions for the encointer types

[clangenb]

Encointer worker has been completely removed here: #116