This introduces a split of the current single ConfigFile instance for
all configuration into two separate instances.
The app config instance contains system-wide settings that mainly
concern the working of the app itself, whereas the user config instance
contains settings actually exposed to the user for the configuration.
c677bac875 changed the order here, but
this also resulted in the string having whatever size was necessary for
the install data path, rather than being large enough to fit a userdata
path. To fix this, move the resize operaetion *after* the buit-in
themes are searched, and also bump it to 1024 just to be sure.
This resulted in a crash due to a bug in os_get_path_internal() which
will need to be fixed separately.
As of 8dcfae9a39, indicating the base
style to the proxy is completely functional.
It also bypasses QT_STYLE_OVERRIDE and -style, but since the system
theme is no longer available on Linux this is a non-issue.
