Volume Renderer v2

[ElpadoCan]

Taking inspiration from PRs #1110, #1102, #1096, #1106, and from https://github.com/keejkrej/acdc-son, this PR implements a 3D volume renderer that can be launched from a Python script (see below), or from the module 3 GUI.

Minimal code:

renderer = VolumeRendererWindow()
renderer.set_volume(zstack_array)   # (Z, Y, X) numpy array
renderer.run()

Features:

• Lut colormap and slider for each channel
• Auto and Reset buttons above each lut slider
• Gamma correction with slider
• Opacity slider for each channel
• Top toolbar with "Home" view and "Save" button
• "Save" buttons saves a PNG screenshot
• Multi-channel overlay
• Overaly segmentation mask
• List of selectable Cell IDs to show only those cells
• Clickable segmentation masks with "Ctrl" click to select more than one
• z-anisotropy correction factor as a numeric control
• z-anisotropy correction factor with the function scipy.ndimage.zoom