New operation status for partial completion

[jnation3406]

For certain operations like median, It would be nice to attempt and produce a result before running out of memory, rather than just letting the operation run out of memory and failing or hanging. We could either add a new status option for partial completion, or just fill in the error message and COMPLETE status to show that it completed with some caveats.

• For Median and Stack operations, load in the images one by one and keep track of their size - when it has exceeded some safe limit we set, stop loading images and process what we have currently loaded
• Once complete, record some note in the "message" cache for the operation detailing what happened ("15/20 images used - memory limit reached") and set the operation to completed with that message and output
• Change frontend to check for the message and if its complete with a message, maybe change the button color or add a "!" icon or something to it to note it had an issue, and show the message on hover-over like we do with FAILED operations.