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 
Yeah, it was copy-pasted, and I plan on improving it. Right now it'll print all C++ classes as simply "userdata:<pointer address>" which is not very useful. I'm going to investigate the best method for getting tostring to work properly for userdata.