Add Snippet File Templates tree view

[RandomFractals]

• integrate it with Auto Snippets extension: https://marketplace.visualstudio.com/items?itemName=Gruntfuggly.auto-snippet
• display configured file globs and snippet mapping from settings.json in that tree view
• display mapped snippet tooltip for preview
• add option to go to autoSnippet.snippets section in settings.json file, or create one
• add option to create new file from auto-snippet template
• add create file template menu option for a snippet tree node in snippets tree view to add new auto snippet for the selected language and snippet