Allowed metadata store

src/api/allowedMetadata.ts

src/api/index.ts

src/api/metadata.ts

src/components/Corpus/AllowedMetaData/CreateForm.vue

src/components/Corpus/AllowedMetaData/List.vue

src/components/Corpus/AllowedMetaData/Row.vue

src/components/Element/Metadata/Metadata.vue

src/filterbar.js

src/store/corpora.js

src/stores/allowedMetadata.ts

src/stores/index.ts

tests/unit/filterbar.spec.js

tests/unit/store/corpora.spec.js

tests/unit/stores/allowedMetadata.spec.js