Instead of one hard-coded theme, support multiple ones
This assumes that the rccs themself contain a /icons/<themename> prefix
To make this usable, we will need to change the way we create the binary resources in breeze-icons and adapt the craft packaging.
Then we can use e.g. breeze + breeze dark for app store applications like normally.
We might want to alter this later to use libs to have mmap on all architectures.
Will alter the initializer before pushing, if it is clarified if the approach is ok.
Given the lack of mmap for resource files on Windows, I actually would prefer to hide the resources in dummy plugins, but I guess it would make sense to do this in a second step.