add api for get/add/update/delete vacancy

[allanwalpy]

all api starts with /api

• POST /api/vacancy - add new vacancy;
• GET /api/vacancy - view all vacancies;
• GET /api/vacancy/{vacancyGuid} - view vacancy;
• PATCH /api/vacancy/{vacancyGuid} - update vacancy;
• DELETE /api/vacancy/{vacancyGuid} - delete vacancy;

Consume: json; Produce: json;

[allanwalpy]

done, with some bugs/workarounds (see #11 ) and with no tests (separate issue #12 )