Using a grid with grouping and selection is totally broken

[aaradi]

I created a very simple Plunker to show the problems: http://plnkr.co/edit/zCstBVfGphTmyXJOYP7h?p=preview
This bug occurs in the latest version, as of today, 4.4.11.
There are a few issues:

1. Select all doesn't select the group headers and vise versa.
2. Selecting a group header and then deselecting one of the selected children doesn't deselect the group header itself.
3. Selecting a few (not all) children under a single group header and then selecting the group header of those children changes all the selected children to deselected and all the deselected children to selected.

[AndreaBittner]

Hi,
I agree to point 1 and 2; I would love to see directly selected or part selected icons in the group headers.
But because I debugged for my use case a bit, I want to add something to point 3, where the behavior is a bit unexpected:

• It is used the function toggleRowSelection(..)* when selecting a grouped Header and toggling based on the selected-value of the row itself.
  Wouldn't it be better to make the toggling dependent of the selected-value of the grouped Header?

Thank you.

_* name toggleRowSelection
@methodOf ui.grid.selection.service:uiGridSelectionService