Added last_login and last_mobile

[MineTech13]

I added last_login to LimitedUser.yaml and last_mobile to User.yaml and tested it for functionality ^^

[C0D3-M4513R]

The fields should then be nullable, right?

[MineTech13]

I believe they can be nullable, as they only appear when a friendship is established.

[VinyarionHyarmendacil]

Strictly speaking, nullable means that the JSON null is a valid value and required means that the key-value pair must be present/defined, e.g.:

	nullable	required	both	neither
{ }	✔️	❌	❌	✔️
{ "key": null }	✔️	❌	✔️	❌
{ "key": "value" }	✔️	✔️	✔️	✔️

[MineTech13]

In that case, it is indeed nullable, as it is only present when "isFriended" is true.