Create Regenerate existing images module

[mxbclang]

Create the initial module infrastructure for the Regenerate Existing Images module. This is required before any further development of the feature can take place. Additionally, as part of this work, the main feature branch feature/regenerate-existing-images should be created for all future work to be branched from and merged into.

Acceptance criteria

• A new folder modules/images/regenerate-existing-images is added to the plugin
• Inside the new folder a can-load.php exists and return an anonymous function
  • The anonymous function returns true for now
• Inside the new folder a load.php file is created and has the correct docblock at the top of the file
• A new feature/regenerate-existing-images branch is created

[felixarntz]

@jjgrainger @ankitrox Leaving 2 minor notes here:

• The can-load.php file shouldn't be needed. It only needs to be present if we actually want to have custom logic, but if we just load this module unconditionally, it's unnecessary.
• Just emphasizing that of course the PR should also be created against that new feature branch :)

[felixarntz]

Fixed via #496