Portability: force wx to use files instead of registery for settings storage on Windows

[MBilderbeek]

See conversation on IRC:

<DeltaRazero> Greetings! Is Catapult capable of reading settings (config, connectors, history, openmsx path) from a local file instead of registry?
<Quibus> Hi DeltaRazero 
<DeltaRazero> As far as I´ve read the doc I´m very sure it can´t, but worth the shot asking
<Quibus> DeltaRazero: catapult uses a storage API of the wxWidgets library
<Quibus> wxConfigBase
<DeltaRazero> ah ok, that tells me enough
<Quibus> The wx library decides where to actually store stuff
<Quibus> Why are you asking? What's wrong with using the registry? Isn't that meant for this?
<DeltaRazero> I like portability of my setups and I actually have two openmsx setups
<Quibus> Docs say:
<Quibus> This function will create the most appropriate implementation of wxConfig available for the current platform. By default this means that the system registry will be used for storing the configuration information under MSW and a file under the user home directory (see wxStandardPaths::GetUserConfigDir()) elsewhere.
<Quibus> We could change it to use wxFileConfig
<Quibus> The doc also says in the next paragraph: "If you prefer to use the configuration files everywhere, you can define wxUSE_CONFIG_NATIVE to 0 when compiling wxWidgets. Or you can simply always create wxFileConfig explicitly."
<Quibus> I suggest doing the latter.
<Quibus> See ConigurationData.cpp/.h
<Quibus> I'm pasting from: https://docs.wxwidgets.org/3.0/classwx_config_base.html#aa7d633935adabe1bf11b5a028f8b3355