Re-added Old Loading Screen JavaScript calls

I've re-added the JavaScript function calls used in Garry's Mod 12 to the loading screen. The following functions were those of which were re-added:
`DownloadingFile( Filename )`
`SetStatusChanged( strStatus )`
`SetFilesNeeded( iDownloading )`
`SetFilesTotal( iFileCount )`

Tests:
http://i.imm.io/10Q0B.png
http://i.imm.io/10Q2q.png
http://samuelmaddock.com/lab/garrysmod/gamedetails.html