Add feature to restore/reset/change password

[oleksandr-romashko]

Related to this issue on the front end: s-rybak/foodies-app#99

• Upon request with a valid email address send an e-mail to the user's e-mail with instructions and a link to restore the user's password. E-mail text should have info to ignore if it wasn't sent by the user. If user/e-mail address wasn't found ...
• Add the possibility to change the user's password upon providing the old password (compare it with the existing password hash) and new password (and maybe a token, or smth else to enhance security and limit brute requests. evaluate an approach similar to e-mail verification).