Subject corpus operations

[osma]

Support for these CLI commands:

• load
• create-subject
• show-subject
• list-subjects
• drop-subjects

(Do we also need an operation for clearing all subjects from a project, without dropping the project? Or maybe the load operation could do that before actually loading anything to the index?)

Plus unit tests and the corresponding REST operations.

[osma]

With the current architecture subjects cannot be modified once loaded. So we don't need the create and drop operations. These should be removed from the Swagger spec and CLI stubs. Showing concepts is still useful though.

[osma]

Done in v0.22, closing.