Allow the user to specify custom snippets

Add a page in the editor settings for specifying custom snippets using Ace's snippet syntax.

You can view the snippet syntax [here](https://ace.c9.io/build/kitchen-sink.html) by scrolling down and clicking "Edit Snippets"

Start by locating the editor settings page and the existing Ace editor integration. Add a settings page or section where users can define custom snippets using Ace's snippet syntax, using the linked Ace documentation as the syntax reference. Done means users can save and use their custom snippets in the editor.

Written by the indexing model from the issue text.