Alloy: Add theme-support for config.json

Alloy's theming-feature is awesome when it comes to branding white-label apps.

However, these white-label apps often also require some contact information and stuff like that to change for each distribution. The most logical place to put these, would be the config.json file. And even for styling, setting some base colors in config.json to use in the TSS is often more efficient then overwriting each color using themed .tss files.

The problem however is... config.json does not support themes.

How about adding support to put a config.json in your /app/themes/myTheme folder, which then would (deep-)extend the base config.json file?