Review the `bp_view` capability support in endpoints

[renatonascalves]

• fixes #496
• adds unit tests
• add support for missing components, i.e., activity

[renatonascalves]

Just a note that the GraphQL API, https://github.com/renatonascalves/wp-graphql-buddypress/pull/124, took a different approach. We don't return an error but rather an empty result. Mainly because in GraphQL, fields can be nested (connections).