[Task] Allow for dynamic definition of custom data types

[CermakM]

User story
As a user,
I'd like to be able to define custom data types,
so that I could, later on, create custom plots for the specific data types.

technical: @CermakM

Acceptance Criteria

• There is a possibility to dynamically define custom data types
• A user-defined data type, when registered, integrates seamlessly with all the existing features
• The feature is documented and the usage is described

Depends on: #16