code-refine preparation & skeleton for dashboard

Signed-off-by: Henry Chen <hchen@vmware.com>
various workflow refactor

1 defer interviewer's selection until interview creation
2 cleanup the interview page, now we assume that the partial 'interviews/_form.htlm.slim' is only loaded
  after opening is already fixed or selected by user.
3 use 'default_scope' for active users' retrieval

Signed-off-by: Henry Chen <hchen@vmware.com>
Merge branch 'master' of https://github.com/vmw-tmpst/heroapp-LetsHire into code_prepare
continue code/workflow refactor

Signed-off-by: Henry Chen <hchen@vmware.com>
Merge pull request #139 from Henry-CF/code_prepare

Code-refine & layout skeleton for dashboard