Design author-related resources to support interactions in the AES

In general, the REST web services must provide capabilities for:

- [x] fetching the list of author types: required to load the options in the corresponding drop-down menus.
```
[GET] /authors/types
```
- [x] searching for authors: required to search on the auto-completion field.
```
[GET] /search/authors
```
- [x] fetching the list of authors for an article: required to load the existing list of authors for the current article.
```
[GET] /articles/{number}/{language}/authors
[GET] /authors/article/{number}/{language}
```
- [x] linking an author to the article: required to add a new author from the existing authors data base to the list of authors in the current article.
```
[LINK] /articles/{number}/{language}
headers:
link: </authors/{id} rel="author">
link: </authors/types/{id} rel="author-type">
```
- [x] updating the author type for an author: required to change the author type for any of the existing authors in the list of article authors.
```
[LINK] /articles/{number}/{language}
headers:
link: </authors/{id} rel="author">
link: </authors/types/{id} rel="author-type">

to update existing article author type just send link request for article with current author and new author type
```
- [x] deleting a single author from the list of authors: required to unlink/remove any of the authors from the list of authors in the current article.
```
[UNLINK] /articles/{number}/{language}
headers:
link: </authors/{id} rel="author">, </authors/types/{id} rel="author-type">
```
- [x] sorting the list of authors: required to order the list of authors in the current article. This action is performed by the user dragging and dropping items up and down within the list.
```
[POST] /articles/{number}/{language}/authors/order

New order must be send with form in this format
    order={authorId}-{authorType},{authorId}-{authorType},{authorId}-{authorType},{authorId}-{authorType}

example:

     order=7-1,8-1,5-2,4-2

All article author-author type pair must be send.
```