Julian Wolff authored May 22, 2019 and Bhushan Shah committed May 27, 2019

The fonts kcm did only parse a local config file. Global and default settings were not recognized.
With this patch, all global config files are parsed before the local file is parsed.
This allows us to drop the "Vendor default" option.

This patch also fixes some changes not recognized (apply button disabled).

CCBUG: 386566

Test Plan:

Delete `~/.config/fontconfig/fonts.conf` and `~/.config/kcmfonts` .
Run `kcmshell5 fonts`. The default/global settings should be displayed.
Change some settings. The apply button should be enabled.
Save. A new config file should be created.

Follow up of the D12925