Add ability to specify alternative text for media attachments (#5123)

* Fix #117 - Add ability to specify alternative text for media attachments

- POST /api/v1/media accepts `description` straight away
- PUT /api/v1/media/:id to update `description` (only for unattached ones)
- Serialized as `name` of Document object in ActivityPub
- Uploads form adjusted for better performance and description input

* Add tests

* Change undo button blend mode to difference

app/javascript/mastodon/features/compose/containers/upload_container.js

@@ -0,0 +1,21 @@
+import { connect } from 'react-redux';
+import Upload from '../components/upload';
+import { undoUploadCompose, changeUploadCompose } from '../../../actions/compose';
+
+const mapStateToProps = (state, { id }) => ({
+  media: state.getIn(['compose', 'media_attachments']).find(item => item.get('id') === id),
+});
+
+const mapDispatchToProps = dispatch => ({
+
+  onUndo: id => {
+    dispatch(undoUploadCompose(id));
+  },
+
+  onDescriptionChange: (id, description) => {
+    dispatch(changeUploadCompose(id, description));
+  },
+
+});
+
+export default connect(mapStateToProps, mapDispatchToProps)(Upload);

app/javascript/mastodon/features/compose/containers/upload_form_container.js

@@ -1,17 +1,8 @@
 import { connect } from 'react-redux';
 import UploadForm from '../components/upload_form';
-import { undoUploadCompose } from '../../../actions/compose';
 
 const mapStateToProps = state => ({
-  media: state.getIn(['compose', 'media_attachments']),
+  mediaIds: state.getIn(['compose', 'media_attachments']).map(item => item.get('id')),
 });
 
-const mapDispatchToProps = dispatch => ({
-
-  onRemoveFile (media_id) {
-    dispatch(undoUploadCompose(media_id));
-  },
-
-});
-
-export default connect(mapStateToProps, mapDispatchToProps)(UploadForm);
+export default connect(mapStateToProps)(UploadForm);