Update datasets task tags to align tags with models (#4067)

* update tasks list

* update tags in dataset cards

* more cards updates

* update dataset tags parser

* fix multi-choice-qa

* style

* small improvements in some dataset cards

* allow certain tag fields to be empty

* update vision datasets tags

* use multi-class-image-classification and remove other tags

Commit from https://github.com/huggingface/datasets/commit/edb4411d4e884690b8b328dba4360dbda6b3cbc8

README.md

@@ -237,19 +237,19 @@ task_categories:
   nc:
   - text-classification
   ner:
-  - structure-prediction
+  - token-classification
   ntg:
-  - conditional-text-generation
+  - summarization
   paws-x:
   - text-classification
   pos:
-  - structure-prediction
+  - token-classification
   qadsm:
   - text-classification
   qam:
   - text-classification
   qg:
-  - conditional-text-generation
+  - text2text-generation
   wpr:
   - text-classification
   xnli:
@@ -262,8 +262,7 @@ task_ids:
   - topic-classification
   ner:
   - named-entity-recognition
-  ntg:
-  - summarization
+  ntg: []
   paws-x:
   - text-classification-other-paraphrase-identification
   pos:
@@ -273,7 +272,7 @@ task_ids:
   qam:
   - acceptability-classification
   qg:
-  - conditional-text-generation-other-question-answering
+  - text2text-generation-other-question-answering
   wpr:
   - acceptability-classification
   xnli: