Bug resolved in displaying audios in e-library

#### Bug fixed ####

* Previously audios were included and displayed under documents section, now query modified according to mime type(audio)
* query made for listing all audios together is : 

**audio_cur = collection.Node.find({ '_type': 'File', 'group_set': {'$all': [ObjectId(group_id)]},  'mime_type': {'$regex': 'audio','$options': "i"} })** 
* for finding the documets other than audio files using mime_type is : 

**import  re
doc_cur =  collection.Node.find({ '_type': 'File', 'group_set': {'$all': [ObjectId(group_id)]},  'mime_type': {'$not': re.compile("^audio.*")} })**

I have specified the query above since this is special case, the only way i found to get the document using mime_type in view files as above. 

#### What is to test ####
* check whether uploaded audio files listing is displayed under audio section in e-library, also check audio files should not be displayed under documents section.