Improve mako config file handling

[dwrth]

I think it would be great if there was a single mako config file where parameters could be overwritten for every theme. In my case I would like to override the border radius.

At the moment I have to dive into the .local/share/ dir to achieve this but it would be much easier to just have one file in my own .config/ where I can make these overrides.

The file .config/mako/config is linked to the respective file in the folder of the currently active theme so any changes made there will only affect the currently selected theme