* refactor: Use flat module list if possible
Before if you wanted to iterate over all loaded modules you had to first
iterate over all blocks and then over their modules even if you didn't
care about alignment.
* refactor: setup modules in separate function
* controller: Print error for duplicate modules
You can't use the same name twice inside the module lists
E.g.
modules-left = a b c
modules-center = a
modules-right = b
would print an error.
We only print an error for now because we don't want to break existing
configs. But in the future this should be properly enforced.
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