Added not_recommended_for_taxon
Merge branch 'master' of github.com:cmungall/uberon
 Added ambiguous_for_taxon. Fixed synclash for spinal cord neuromere
     * Added ambiguous_for_taxon annotation property - applied to serial digits for aves
     * Neuro
       * Adding Cumbo defs and subsets. Addresses issue #320
       * NTs for prosomere and mesomere, not clear if these will remain. See issue #318
       * Added multiple NN xrefs
     * tagged homology with subsets
     * removed homology logical assertions for procoracoid and scapular spine based on review by Phenoscape AD/PM. Addresses issue #319
     * merged future {corpus striatum, caudate nucleus} into the generic structure
     * NT: {left,right} crus of diaphragm
     * relabeled median umbilical ligament -> remnant of urachus
     * NTs for palpebral vein/arteries
     * Made groove a feature of a tissue (anatomical structure). Created separate class for groove qua line (not clear if this is useful). Addressses #314
     * classified digestive tube junctions as anatomical junctions (material) rather than boundaries (immaterial). Fixes issue #314