Stop using $HOME/.zen for config

[RaphGL]

I know that violating XDG standards and other OS standards is almost "standard" itself. But if possible, I'd like to see the browser respecting it. So instead of having $HOME/.zen for config instead do:

• Linux and other XDG compliant OSes: $XDG_CONFIG_HOME/zen (if empty it's $HOME/.config/zen)
• MacOS: $HOME/Library/Application Support/zen
• Windows: %AppData%\zen

[0xEDApps]

the problem in windows is that it uses %AppData% from the registry, not the environment.
on top of that it uses two locations (roaming and local) and the registry itself, not only creates a zen folder but also a mozilla folder, that might interfere with other installations like firefox.
C:\Users\XXX\AppData\Local\Zen
C:\Users\XXX\AppData\Roaming\Zen
C:\Users\XXX\AppData\Roaming\Mozilla
and this:
HKEY_CURRENT_USER\Software\Mozilla\Zen
should be:
HKEY_CURRENT_USER\Software\Zen
or not exist at all