Add our annotations to the API docs

[Cervator]

Follow-up after #2143 and part of #1975

We now list all @API flagged classes & packages + our whitelist. One remaining thing I think we should highlight in its own section are our custom annotations like @Command

I think most/all are already covered by package declarations like org.terasology.logic.console.commandSystem.annotations (PACKAGE) but I think they deserve individual mention as available annotations so we can have direct links to the javadoc for each annotation right on the main page.

This could perhaps be argued better as its own export since some annotations might only make sense in the engine when configuring some things. I am unsure. I see 44 annotations at present.

After this is complete the Modding API page in the wiki should be updated, just as after #2143 (which I did before submitting this)

Pinging @MaloJaffre if interested :-)