Refactoring cavities and linings to conform to a standard design patt…

…ern, and clearing up many confusions. Fixes #86

preparing for obsoletion of 'cavity lining' and 'cavity or lining'. These have more precise concepts (serous sac and serous membrane)
NT: serous cavity
Using luminal_space_of pattern for cavities
Ventral body cavity: now JEPD pattern for thoracic/abdominopelvic
Coelem and cavity fixes
pleural cavities
NT: visceral fat
NT: *cardial fat