[SHACK-187] split en.yml to separate errors out from application messages

[marcparadise]

Description

This makes en.yml a little less unwieldy by splitting it:

• application messages: i18n/en.yml
• error messages: i18n/errors/en.yml

Signed-off-by: Marc A. Paradise marc.paradise@gmail.com

Check List

• [x] ~New functionality includes tests~ (na: no new functionality)
• [x] All tests pass
• [x] PR title is a worthy inclusion in the CHANGELOG
• [x] You have locally validated the change