For segment, circle, beziers, these are the same in all editors and only
need access to the EDA_SHAPE nature, so we can remove the duplication
entirely.
For TABLECELLs, while the cells are polymorphic in that PCB and SCH
cells are both EDA_SHAPEs (via the TEXTBOXes), the parent TABLES
are not polymorphic, and thus the implementation can't be trivially
de-duplicated. Rather than do something with templates, just keep
it simple for now and maybe look at unifying tables later on.
