added few classes from Core

Author: cmllezr

src/ontology/imports/pmdco_terms.txt

@@ -22,3 +22,6 @@ https://w3id.org/pmd/co/PMD_0000882 #phase boundary
 https://w3id.org/pmd/co/PMD_0000777 #heat capacity
 https://w3id.org/pmd/co/PMD_0000949 #stiffness
 https://w3id.org/pmd/co/PMD_0020202 #crack
+https://w3id.org/pmd/co/PMD_0020000 # thermodynamic phase
+https://w3id.org/pmd/co/PMD_0020160 # 'microconstituent (phase mixture)'
+https://w3id.org/pmd/co/PMD_0000857 # microstructure