All: Added support for hierarchical/nested tags (#2572)

The implementation uses / symbol as a nesting separator. I.e. tag/subtag is a nested tag, where tag is the parent tag and subtag is its child. Creating a tag named tag/subtag/subsubtag creates three tags, one for each level. The tags are associated using parent_id field.

In the app, viewing notes with a tag will also show all notes that are associated with any of the tag's descendant tags (same for the note count). Deleting a tag will also delete all its descendant tags.

In the desktop app the tags are shown nested just like the notebooks.

ReactNativeClient/lib/nested-utils.js

@@ -0,0 +1,22 @@
+/* eslint no-useless-escape: 0*/
+
+function nestedPath(items, itemId) {
+	const idToItem = {};
+	for (let i = 0; i < items.length; i++) {
+		idToItem[items[i].id] = items[i];
+	}
+
+	const path = [];
+	while (itemId) {
+		const item = idToItem[itemId];
+		if (!item) break; // Shouldn't happen
+		path.push(item);
+		itemId = item.parent_id;
+	}
+
+	path.reverse();
+
+	return path;
+}
+
+module.exports = { nestedPath };