Add new parameters to Group Layer for the z_depth visibility feature
Add new members to ContextParams to include the z_depth range visibility.
When optimizing layers only add the layers that are visible in the range.
Move the new parameters description below the set hidden for outline_grow
Layer: Add member to calculate the true z depth of the layer.
Use it where applicable
Add member to retrieve the z_depth visibility (0.0 - 1.0 float range)
Fix bounding box for Paste Cavnas Layer when z depth range is enabled.
Fix hit_check and get_color to properly work
with Paste Canvases with layers with z depth range enabled.
WIP: Use recent implemented z_depth_visibility when optimizing layers
Use the transition parameter to make layers partially visible in the transition area.
Make z_depth range enabled parameter static.
Structure for new action "Layer ZDepth Range Set"
Remember the position and depth of the z_depth from the selected layers
Laeyr: Add member function to find the handle of its parent Paste Canvas Layer
or NULL if it belongs to root canvas
Consider included in visible range layers placed on right boundary too.
Default z_depth_range_depth to be 0.0
Various fixes to make Layer ZDepth Range Set work.
Action is not candidate if layers are in root canvas.
Calculate properly z_depth_range_depth value to set.
Action is ready if there isn't new calculated z_depth position.
Add actions to change the Layer PasteCanvas parameters.
Add some warnings to explain why the paste canvas is not found.
Make the action not ready for exported canvases
Z Depth visible layers are shown with bold letters in the layer panel.
Fix visibility of Layer_PasteCanvas.
Fix wrong signal connection.
Try to update layers bold letters when parameter is modified by hand on the parameters panel.

Seems to not work either. The LayerParamTree::on_layer_z_depth_range_changed handler seems to do not do the right thing.