Made SDK.bat/sh and Build.bat/sh more dynamic.  SDK.bat/sh now lists out the possible choices based on the files in the ../makefiles/sdk/ directory.  Build.bat/sh now lists out the possible choices based on the ../sdks/ directory.

../makefiles/game/ was changed to ../makefiles/sdk/ to support the new changes in the SDK.bat/sh files.  csgo.usermessages.cmake was moved to a directory inside the ../makefiles/sdk/ directory so that it would not be listed by SDK.bat/sh.