Presentation bug fix

Hi all,

 If you've ever met the problem of abnormal filename in presentation window of bbb, like using“-” to replace the non-ascii character in filename, or if your txt file display the wrong character set, try the patches here: https://github.com/fuji246/bigbluebutton， or you can try the test site, http://www.commuxi.com. 

 Welcome your feedback and suggestions.