Minor code cleanup
Tweak Config system to enable correct handling of nested categories

The configuration system will now correctly show nested categories within the
configuration gui, and will also localize the category names depending on the
language file present. Also a change to the config file to use a single
Astronomia.cfg file within the root of the config directory, rather than one in
it's own directory, this may change in the future if necessary for additional
functionality.
Add ModItemRegistry class, a container class for mod items/blocks

Added a new class, the ModItemRegistry, which includes a set of helper
functions and is intended to be used to contain the various items and blocks
that a mod has. There are a couple helper functions added to facilitate easier
adding and initializing the mods and items. This also has the added benefit of
automatically adding it to the configuration file with added localizations for
the configuration gui.
Add Creative Tabs for Blocks and Items

Created 2 creative tabs for blocks and items, and initialized them within the
game.
Add registries for mod items and blocks

Created new registries to hold the mod items and blocks, there may be more
added in the future to help keep like items and blocks together, but for now
this basic separation of them will work fine.
Add the first item to the game

This first item will be the base for the start of the research system. It will
be used for looking up into the night sky so you can make drawings of the stars
and other celestial objects. Right now it doesn't do anything, just having
placeholder functionality, and having no texture, but it will take some time to
work out how to get it all working.