- echo is now on v4 with major changes including a few breaking changes
- bind() behaviour is now strict. JSON / form etc. unmarshalling of
request data need appropriate `json`, `form` tags. Missing tags for
the public subscription page is added in this commit.
- This also closes#602.
- Refactor subimporter New*() funcs to take opt structs.
- Refactor and simplify Vue code.
- Remove redundant i18n entries and use existing ones.
- Remove redundant subimporter constants and use existing ones.
- Consider 'overwrite' option for subscription status as well.
- Write Cypress integration tests for the new feature.
