Generate cover image (#376)

* Make mutating metadata ops mutation
* Implement scene generate screenshot
* Remove fetch policy on metadata mutations
* Port UI changes to v2.5
* Set generated image in database

graphql/documents/queries/settings/metadata.graphql

@@ -1,27 +1,3 @@
-query MetadataImport {
-  metadataImport
-}
-
-query MetadataExport {
-  metadataExport
-}
-
-query MetadataScan($input: ScanMetadataInput!) {
-  metadataScan(input: $input)
-}
-
-query MetadataGenerate($input: GenerateMetadataInput!) {
-  metadataGenerate(input: $input)
-}
-
-query MetadataAutoTag($input: AutoTagMetadataInput!) {
-  metadataAutoTag(input: $input)
-}
-
-query MetadataClean {
-  metadataClean
-}
-
 query JobStatus {
   jobStatus {
     progress
@@ -29,7 +5,3 @@ query JobStatus {
     message
   }
 }
-
-query StopJob {
-  stopJob
-}