Add "Company" component to data model

[brylie]

Urban design involves public and private-sector entities. Companies are often responsible for actual development of design projects, whether on the scale of individual housing units or city-wide utilities.

Need

We would like to document companies who are related to sustainable development initiatives.

Design

Companies should have the following attributes:

• name
• description
• website
• logo?

Companies may be based on the generic Group class #155

Companies can be related (many-to-many) to Projects and possibly Groups.