init commit for schedule interviews

Completed List:
 Front-end
 1 add/delete table rows;
 2 scheduled_at time picker functionality is able to work, (need more twist for display  consistency);
 3 submit and redirect once succeed.

  Backend:
  1 save API with transaction support


To-do-list
1 how to give validation error;
2 interviewer's selection dialog and back-end saving;
3 candidate/opening's pre-select before show/editing 'schedule interviews' table.