add dendrogram selection on 2D image viewer

[PennyQ]

as above, it now an icon on 2D image viewer.

[PennyQ]

@astrofrog How to get dendrogram structure within ImageWidget? data['structure' will return a ndarray not a real dendrogram object.

[PennyQ]

data = self.widget.client.display_data -> data which returns a datacollection
check label='dendrogram' for later

[PennyQ]

I guess we need all 'children' instead of 'parent', I know 'child' is not in the data object, keep it like this first? (see the figure below)

Icon is still not shown as checked yet, what's the size of it again, 72*72 + alpha channel? maybe I could make another one ;)
@astrofrog

[astrofrog]

@PennyQ - it should be easy to find the children given a structure. Given a structure idx, you can find its children (it might have several) by doing (I think):

children = np.where(parent == idx)[0]

[astrofrog]

So then given a structure, you need to loop recursively over all the children of a structure in order to select the whole structure.

[PennyQ]

@astrofrog It's updated with 1) finding all children branches 2) add mouse dragging to extend selection 3) update with a new icon figure
One todo should be now show the icon if there is no dendrogram file. I will think about adding it to 3D viewer after this is merged ;)