FEATURE #553 [SnippetBundle] Possiblity to show all snippet types

Default behavior when no snippet type is selected is now to show all snipet types.

_Tasks:__

- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | ywa
| Fixed tickets | #553 
| BC Breaks     | Default behavior is now to allow selection of all snippet types (instead of falling back to restricting on the default snippet type)
| Doc           | 
yeah. the question is where etc. I guess for now I will put it in `FOUNDATION`. But I think we should really think about starting a dedicated documentation project in `rst` format, or expand the existing docs by @danrot to have both User and Developer documentation "books".