[FEATURE REQUEST] Add Message Extras support

[0PandaDEV]

It would be very useful to have the ability to use message extras from gotify especially the click.url.

https://gotify.net/docs/msgextras

[androidseb25]

It's an iGotify App Feature request so i tagged it for iOS.
i see what i can do to implement it under iOS

[androidseb25]

moved to the next dot release, canceled in 1.5