osx: show testnet icon in dock as early as possible #2614

A green testnet splashscreen with a normal, orange dock icon looks strange and can confuse users.

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Idea is good, but I dislike the fact that this is a) Mac only and b) we have that stuff as duplicate in void BitcoinGUI::setClientModel(ClientModel *clientModel). Even on Windows we first have that normal tray icon and after loading it switches to testnet. I think it's worth to think about a better solution that covers all OSes and directly displays the correct icon.

We currently set the default icon in the BitcoinGUI constructor, where we don't have acces to clientmodel, which is used to query for testnet later... see the problem? @laanwj Do you have a good idea?

@diapolo The reason for this appears to be that on MacOSX it shows the dock icon already before the main window (and tray icon) is created, immediately at the start of the process. This has no analog in any other OS.

It is usually desirable to move the common code to a function, but in this case it's only one line (and result purely visual) so I'm not so sure.

On windows/linux it would be possible to change the icon a little bit sooner (ie, immediately when creating the main window) but mehh. It's only testnet, only developers get to see it anyway. Don't obsess about it too much.

As @laanwj said: it's devs only stuff. But I also agree with @Diapolo: we should also take a look at win and Linux. I do not have a win toolchain,... so @Diapolo your probably the right guy for a win optimization of that issue.

At least on Windows I get a tray-icon directly when the splashscreen is doing it's work and have our mainnet icon, before it get's switched to the testnet one... I think that is rather ugly ;) or at least not perfect ^^. So I asked for a global solution :).