Fix duplicate email bug

[pierreTklein]

Tickets:

HCK-185

List of changes:

Added check to updateAccount middleware to see whether or not the new email already exists in the database, and if so, return a dup email error.

Error should now be: "Email already in use"

Type of change

• Bug fix (non-breaking change which fixes an issue)

How has this been tested?

Ran test suite

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have made corresponding changes to the documentation
• Any dependent changes have been merged and published in downstream modules

[loreina]

🎉 🎉 🎉

[loreina]

closes #619