audio: fix recording

Audio recording files are not closed properly, making them corrupt
on mac osx (wave header for file size or duration is 0) . Also
recording filenames contain duplicates, and sometimes missing
the entire filename.

This patch :
- adds call to closeFile when a call is remove from manager
- prevents filename duplication
- ensures filename is initialized on audio recorder

Change-Id: Iec3a606f9e65bbbfb5bcaf50ba924223c396507b
Tuleap: #999