ContentDB: Add support for package aliases / renaming

[rubenwardy]

This allows users to change their usernames on ContentDB, and transferring packages between authors.

Here is GreenDimond renamed to GreenXenith

To do

This PR is a Ready for Review.

How to test

I don't want to introduce aliases to production ContentDB until 5.5.0 is released and mod authors are happy to only support 5.5.0+, as this will cause installs to no longer detect updates on older versions.

I tested locally using a development version of ContentDB. However, you can test by installing on of GreenXenith's mods and then adding the following to dlg_contentstore.lua:570:

if package.author == "GreenDimond" then
	package.author = "GreenXenith"
	package.aliases = {
		"GreenDimond/" .. package.name
	}
end

[SmallJoker]

LGTM