Implement a stdlib API

# A complete stdlib API
This pull request adds a complete, working and fully-usable stdlib API for complex usages. It features release management, retrieval of published releases and acceptance or rejection of suggested libraries for the stdlib.

It replaces the almost unusable current way where a lib either has the `default_include` attribute or not.

## Todo
### Release management
- [x] list releases
- [x] create release
- [x] publish releases
- [x] delete unpublished releases
- [x] describe releases
- [x] modify unpublished release metadata

### Candidate acception
- [x] See #25 (must be merged in here before this PR can be merged).

### Pending items
- [x] See #28 (must be merged in here before this PR can be merged).

### Items
- [x] List items in any stdlib release + including releases

## Documentation
Alongside with development on this, the WIKI documentation is updated. See [here](https://github.com/maul-esel/ALD-API/wiki/Stdlib-API).