Limit size of changelog.json

[AlexCPU]

When starting a new instance with no previously downloaded assets, the changelog.json lists every single image that has been downloaded. This causes changelog.html to contain 1.1GB of images when loaded into a browser. This feels like a bad idea!

Propose that if latestVersion.txt is blank/doesn't exist (i.e. this is the first run), that we generate an empty changelog.json, such that next time there are changes, these are the first to be captured.

[AlexCPU]

Also, we should limit the number of entries in the changelog.json so it doesn't get unwieldy over time. Seeing how this functionality is mostly used by people checking on names or paths of new assets, the last 10 updates would be my proposal

[ineffyble]

@AlexCPU Is this still outstanding?

[AlexCPU]

Yep, everything above is still true.