FR: add per user pincodes

[Mariusthvdb]

As already discussed in previous FR:

If anyone wants this:

code: 
  - user: aaaa1234567890
    code: 12345
  - user: 1234567890aaaa
    code: 00000

please let me know in a separate FR.

Originally posted by @ildar170975 in #67

the advantage here is the admin can set a unique code per user, opposed to a generic global set of pins that all users can select from.

makes it more specific, and (I hope) just a bit more secure.

[ildar170975]

I will think about it. But this may not be quick.

[Mariusthvdb]

hehe, ok!
since you asked for it, I thought to write it up ;-)
take your time