Update message catalogue for SUBFLOW UI

[HiroyasuNishiyama]

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

Message catalogue entry for editor.types.cred is referenced but not defined.
This PR adds definition entries for en-US & ja locale.

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the mailing list/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality

[coveralls]

Coverage remained the same at 77.438% when pulling 2da1554 on node-red-hitachi:update-message-catalogue into 4f9395e on node-red:dev.

[knolleary]

Ooops - missed that. Thanks!