Include snippets in references shown at method removal

[zeniko]

Before removing a method, GT informs about how many references to that method are left. These are however only references from code in the Coder, not references from Lepiter snippets.

Since these snippets can be also be filtered (for "References in snippets"), why not also show them before removing a method? This would help to prevent accidental breakage when refactoring/cleaning up code.

[girba]

The basic infrastructure exists, but we do not yet have a consolidated way to search for both.