Blocks for block-based image processing (WIP).
Allow variables to be set to Images.
Add _format function for ExperimentProtocol.
Fix error in Variables.add().
Move Image data and ImageProvider into octopus.
image_tonumber outputs a number.
Block-based image processing.

- Uses octopus camera devices to provide image data.
- Image processing blocks added.
- image_tonumber block can extract blob height, width, x or y position.
- Image display functionality for image variables in the experiment
viewer.