Add support for server 4.2.0

[ulu]

After updating the server from 4.1.0 to 4.2 I'll get some warnings regarding incompatibilities of grocy-android.

Would it be possible to make grocy-android compatible again?

[Gerben321]

As far as I can see it is compatible, I haven't found anything strange. So removing the warning would be great for sure.

[patzly]

Here is an answer to that, with the update that we both have a full-time job now: #558 (comment)

We notice ourself when a new Grocy version is released but an update simply needs time, so no extra issue is required. Otherwise all incompatibility issues are very welcome.