Return all fetched messages headers in JSON.

This is in preperation of BIMI-Selectors #1394

dev/Model/MimeHeaderCollection.js

@@ -0,0 +1,32 @@
+import { AbstractCollectionModel } from 'Model/AbstractCollection';
+import { MimeHeaderModel } from 'Model/MimeHeader';
+
+'use strict';
+
+export class MimeHeaderCollectionModel extends AbstractCollectionModel
+{
+	/**
+	 * @param {?Array} json
+	 * @returns {MimeHeaderCollectionModel}
+	 */
+	static reviveFromJson(items) {
+		return super.reviveFromJson(items, header => MimeHeaderModel.reviveFromJson(header));
+	}
+
+	/**
+	 * @param {string} name
+	 * @returns {?MimeHeader}
+	 */
+	getByName(name)
+	{
+		name = name.toLowerCase();
+		return this.find(header => header.name.toLowerCase() === name);
+	}
+
+	valueByName(name)
+	{
+		const header = this.getByName(name);
+		return header ? header.value : '';
+	}
+
+}