Refactor glyph info lookup

I just had a look at the way the glyph info is generated (from looking at Jans pull request [#778](https://github.com/googlefonts/glyphsLib/pull/778)).

There are two (or three) function that do ligature lookup (in `_construct_production_name`, `_construct_category` and soon `_construct_script`). I would recommend to put the fallback into `_lookup_attributes` (or make a new one like `_lookup_attributes_with_fallback`). So that it returns the needed attributes for all names that it can recognize. (or rename `_lookup_attributes` to `_lookup_attributes_data` and make a new `_lookup_attributes`)

I can have a look when the pull request is merged.