NodeTreeWidget: Add input nodes

[danielhollas]

Currently in the tree, we only show the output nodes in the outputs directory of a given workchain. Sometimes it is very useful for debugging to see exactly how the input nodes look like. Therefore I propose we add the inputs directory.

This should be relatively easy, we just need to generalize the code that adds the output nodes.

aiidalab-widgets-base/aiidalab_widgets_base/nodes.py

Line 102 in 149a249

class AiidaOutputsTreeNode(TreeNode):

See also corresponding discussion on the QeApp.
aiidalab/aiidalab-qe#352

[danielhollas]

@unkcpz any thoughts on this? I think I'd like to tackle this in a relatively near future. I need to solve some performance issues with the NodeTree widget, and this looks like an easier issue to tackle first to get familiar with the widget.

[unkcpz]

That would be great if you can have a look at it! I need to remind the variable naming convention is very nasty in this widget, maybe you can start from standardize it. The "node" of the node tree is confusing with the AiiDA node concept in this widget, which makes it very buggy.