Fixing the build scripts
* Rewrote clean_build.bat. It was deleting all the scripts in the build scripts folder >:[
* Fixed the build_unity_client.bat to create the build\client folder if it's missing
* Fixed the copy_content_to_build.bat to create the build folder if its missing
* Fixed the copy_server_dlls_to_unity.bat to create the unityClient/Assets/Plugins folder if it's missing
* Removed the Plugins.meta file since that folder should only exist after the build scripts
* Fixed paths in MobTypeManager and RoomTemplateManager