Fixes broken behaviour of list.groups

list.groups doesn't seem to behave as expected (at least by me):

> list.groups(hdf5file, path = "/annotations", recursive = F)
[1] "/annotations/info"          "/annotations/objects"       "/annotations/annotations"   "/annotations/events"        "/annotations/tracklets"     "/annotations/autotracklets"
[7] "/annotations/images" 

So apparently, only the groups of the .Object (first argument) are appended to the given path. To fix this, you can just use the subscript operator like this:

> list.groups(hdf5file["/annotations"], recursive = FALSE)
[1] "/annotations/object_annotations" "/annotations/track_annotations"

Which gives the expected result.

This merge request includes this fix in all places that utilise list.groups.