[REVIEW] Fix hash vulnerability when generating password recovery

[WelisonR]

Description

This pull request fix a vulnerability in the generated hash used to recover password. The main problem is that the hash input is known, because it is only based on timestamp and user e-mail, so with some attempts it is possible to change the user password. The code also uses MD5 hash function to generate the hash, that has a lot of vulnerabilities known today.

Resolves (Issues)

Resolve #416

General tasks performed

• Add a random argument to hash input with secrets library;
• Change MD5 hash function to SHA256.

Have you confirmed the application builds locally without error? See here.

• Yes

[vjpixel]

I'm waiting for it to be live on dev.jandig.app so I can review it from a user perspective.

@pablodiegoss