Add option to disable default/all snippets

Suggest either making editing default snippets easier by separating them from the default packages, or adding a setting to disable those or all snippets altogether.

Pre-built snippets are not always useful. When they are not, they become a nuisance when user is using tab to complete keywords in the current file. E.g. trying to complete keyword 'proto' in a JavaScript file becomes impossible, as a pre-built snippet already exists with that name.