Keep the deep_morph structure intact when resolving MWU's

[kosloot]

When resolving MWU's (in frog_data::resolve_mwus() ) the deep_morphs structure is lost; only the deep_morph_string member is resolved. This is disadvantageous, as it is impossible to retrieve the separate deep_morphs and inflections from MWU's (without stupid split() actions). This especially a problem while creating JSON output. TODO: rework MWU resolving keeping the parts available.