BUG? Space support in attachments

[MvantLoo]

When you upload an attachment with spaces in the filename, you will see the md-string in stead of the download link.

I solved this in file Document.class.php by adding rawurlencode():
Line 299: $attachment->url=PATH."datasets/documents/".$this->ID."/".rawurlencode($element_fe);

Also a sneaky request to support txt files ;) or maybe better: use a setting for a list of allowed file-extentions.
Line 295: if(!in_array(end($file_extension),array("pdf","doc","docx","xls","xlsx","ppt","pptx","txt"))){continue;}

[Zavy86]

fixed in #275