fix: Properly handle image files

[juliushaertl]

Fix #56

So far the basics are working but requires some cleanup and edge case handling

• Basic fetching of images through websocket
• Push new images to websocket
• Read images from file content
• Store images in memory and persist them on write
• Properly cleanup images that are removed
• Make sure that only updated data is transferred
• Cleanup code

[juliushaertl]

This is ready for review and some testing from my side. There might still be some room to optimize further but this should be good enough as a first approach to get images working.

@hweihwang Could you give it a try as well? Would be great to get some feedback on the implementation from you :)