Draft: First attempt loading simulator image from a URL

URL kwarg for the simulator so we can look at something more interesting than generated black blobs

This MR contains the following

• Simulation json has a URL pointing to an example JPEG
• Simulated camera has a URL argument

Before merge:

• Full tidy, this isn't ready to merge
• Do we want to host our images?
• Drop down menu for images?
• Open images from device?
• Back up generated sprites
• Why does it crash when reaching the end of the canvas?
• Ben and I saw one loop round - going so far right that we ended wrapping round to the left

Merge checklist:

• All new/changed functions have up to date typehints and docstrings
• Any UI updates have a before and after screenshot in the MR description
• Unit testing of new functionality has similar or better coverage that similar existing code
• This code has been tested on a microscope
  • With webapp has been recompiled (if changed)
  • With updated settings JSON (if changed)
  • SmartScan and live stitching work