Revert DLC cooking + some improvements

[Xymanek]

This reverts the DLC cooking approach (#46) and also implements some improvements to the previous/original approach:

• The asset cooking step is split into a separate class (and more methods) - it was getting too big. Hopefully it will be much easier to read/follow the logic now
• There are no more "native package cannot be cooked but that's fine" messages
• All original always loaded objects (native script packages + startup + their references) are now properly marked as such
• The previous 2 points are achieved by caching the script packages built in release mode and some config/timestamp manipulations
• More diagnostic output
• Fixes #13
• Resolves #9
• Resolves #11

[Xymanek]

If you specify a map in sfMaps, there's no warning or error that I can see (it does error if an sfStandalone package is missing

Both are "checked" when the cooked packages are copied to the staging directory. If the source packages don't exist the cooker won't produce a cooked one, so Copy-Item will fail