Redefining the realizer feature

[aerugo]

We want to move Realities away from individual realizers to a more group-based approach.
In addition, we also want to simplify the system by only applying realizers to Responsibilities and not to Needs. Needs should only have guides.

• Allow assigning multiple realizers to a responsibility Allow adding multiple realizers to a resp #212
• Remove the realizer field from needs Remove certain fields from Needs, e.g. Realizers #211
• Guides remain unchanged - only one guide per need or responsibility

[Powersource]

Split this into separate issues, see links in original post