Lua: Core improvements

The goal here is to make FF's Lua environment more robust while maintaining backwards compatibility.

The most important stuff so far (from a commit message):
* Backport a lot of the changes to the script manager made in the 2013 port
  * Make Lua's 'print' function redirect to the console
  * Add lua_dostring server command that will attempt to run the given string in the global Lua environment
  * Expose all safe default Lua library functions (newly exposed packages: package, debug, os)
  * Make Lua's 'require' look in ModDir/maps/includes, ModDir/maps/ and ModDir/ when resolving modules
* Remove unused CRC32 script validation system
* Standardize Lua console messages/warnings 

Some stuff that I'd like to do:
- [x] Deprecate and/or make `IncludeScript` use `require`
- [x] Add `tostring` support for userdata so that, at the very least, userdata prints something like `<entity_classname>:<memory_address>`