Clients do not need all server pip packages

[maaktweluit]

As a task-api library i want to specify different dependencies for clients implementations and server implementations so the client can be light.

Caused by #67
Patched in #71

Make peewee a dependency of task-api-server imports and not of task-api client imports.

• Split packages in 3 ( core / client / server )
• Make server a feature that installs extra dependency ( like in rust )
• TBD

[maaktweluit]

+1 for split into 3.

Later we want the dependencies ( able to be ) split by the 3 users of the task-api library:

• Requestor image
• Provider image
• client implementation in golem core