Prevents a massive inload of Scrumplex ditto's :)
I didn't add it to every file modified in this PR because the other
changes are pretty minor, and would explode the diff of the PR. I hope
that's not a problem O_O
For now this doesn't mean much, but it will help when we need data
exclusive from the metadata, such as addon id and mod provider.
Also removes the metadata when the mod is deleted, and make the Mod.h
file a little more pleasing to look at :)
