[Examples] Refactor p/demo/blog package to use slice instead of AVL tree

[leohhhn]

Description

Currently there is an unsolved bug with AVL Tree: #2266 & #1543

This makes the edit & remove functionalities in the blog package unusable. I propose that we refactor this package to use slices; AVL Trees are very good at storing large amounts of nodes (in this case, blog posts); in the case of the blog package, the amount of blog posts will realistically not be large. I propose that we replace the AVL tree storage with slices, so that all of the aforementioned functionalities are working properly; at least until we fix the bug.