Fix encoding menu in file node

[kazuhitoyokoi]

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

Proposed changes

Current encoding menu in file-in and file-out nodes doesn't have title, "Encoding" because message catalog doesn't contain the message. Therefore, I added the messages into the catalogs.
Simultaneously, I added visible/hidden handling in encoding menu when Node-RED user selects "delete file" in Action menu.

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 decreased (-0.03%) to 76.433% when pulling 0f57d1a on kazuhitoyokoi:master-fixfilenode into 63829b6 on node-red:master.

[kazuhitoyokoi]

@knolleary Thank you.