[47124347] standardize error message formatting

Errors with inputing data, like invalid email, should show flash message
at top (There was an error with your data), and a specific message to
the right of the input field (This is an invalid email).

Signed-off-by: Henry Chen <hchen@vmware.com>
Merge pull request #59 from Henry-CF/style

[47124347] standardize error message formatting
[47124483] tune-up the 'new candidate' page

Only departments that contain openings are available for choose.

Signed-off-by: Henry Chen <hchen@vmware.com>
Merge branch 'master' of github.com:vmw-tmpst/heroapp-LetsHire into style
Merge pull request #60 from Henry-CF/bugfix

[47124483] tune-up the 'new candidate' page
[47351445] ensure children are deleted when deleting parent

define some 'has_many' association as composition.
also fix an 'Are you sure' prompt twice issue in development mode.

Signed-off-by: Henry Chen <hchen@vmware.com>
Merge pull request #61 from Henry-CF/bugfix

[47351445] ensure children are deleted when deleting parent