KAZOO-1856: supress warnings about templates
KAZOO-1856: remove cb_context access from cb_vmboxes
KAZOO-1856: clean up setting charset on email
KAZOO-1856: properly set the extension of the voicemail

Use either the media_type from the media doc, or the content_type from the
attachment, to get the extension for the attachment.
KAZOO-1856: remove warnings about unused vars
Merge pull request #294 from 2600hz/KAZOO-1856

Kazoo 1856