[RestResourceIncidentTracker] Allow empty password

Because it's not needed when a user choose to use API key for
authentication. I'll remove the password entry from UI and force
use API key by default for Redmine.
[HatoholIncidentTrackerEditor] Always hide password entry

Because we always use API key for Redmine, and we support only
Redmine at this time. So we don't need the password entry.
[HatoholIncidentTrackerEditor] Fix a comment
[HatoholIncidentTrackerEditor] Expand the width of label area

Because it's a little narrow for Japanese
[HatoholIncidentTrackerEditor] Switch the label for user name entry according to the state of password entry
[HatoholIncidentTrackerEditor] Switch the label for user name correctly

There is a bug in the previous commit.
[HatoholIncidentTrackerEditor] Use suitable label on showing a validation error of API Key
Merge pull request #469 from project-hatohol/modify-redmine-auth

Modify redmine auth