read_grammatical_expressions shouldn't need universe as argument anymore

[haberchr]

It seems now that reading expressions requires again that Universe be specified upon loading them. After an initial refactor of Meaning, it looks like Universe had not been required for loading Meanings for a bit. Since Expressions need a meaning, this means that requiring Universe in Meaning once again means that loading expressions requires defining a Universe in a function that loads / reads the expressions. However, because Expression has a Universe as an attribute, it is saved in the yaml dump and should not need to be specified as an argument in functions that load expressions.

A potential solution could be to load the first Expression's Universe attribute in read_grammatical_expressions and use that instead of passing universe as an argument in that function.