Fix emoji and number layouts

They stopped working due to https://source.puri.sm/Librem5/squeekboard/-/merge_requests/437

There's also some cleanup: there's no need for a separate fallback for the terminal, and there's no need to handle terminal separately from other "purposes". Numbers want to be language-dependent too.

In addition, layouts will be searched for in subdirectories, making the handling of separators consistent.