Add profile picture uploading functionality

Purpose

The purpose of this PR is to fix #26

Add profile picture uploading functionality
Approach
Update relevant controllers
Use multer to handle file uploading
Fix user registration issues
Checklist
[x] This PR doesn't commit any keys, passwords, tokens, usernames, or other secrets.
[ ] I have read and understood the development best practices guidelines ( http://bit.ly/sef-best-practices )
[ ] 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
[ ] I have made corresponding changes to the documentation