Create entity type store

src/api/entity.ts

src/api/entityType.ts

src/api/index.ts

src/components/Corpus/EntityType/CreateForm.vue

src/components/Corpus/EntityType/List.vue

src/components/Corpus/EntityType/Row.vue

src/store/corpora.js

src/stores/entityTypes.ts

src/stores/index.ts

tests/unit/store/corpora.spec.js

tests/unit/stores/entitytypes.spec.js