Chore/add missing parts emails

# This pull request involves:

* Adds kardex in subject of mails
* Fix failing tests
* Adds link to admin area in kardex

## Description

I add to the emails a link to admin area, also the subject of the email contain the word kardex, fix the failing tests and add the default URL option to mailer in development environment.
Prefer double-quoted strings unless you need single quotes to avoid extra backslashes for escaping.