Add feature to overriding the Mime type check for .mp4 when the user is sure of its file

At least on Windows I got multiples times a detected type of 
`inode/blockdevice`. In reality files where good mp4 files accepted by 
peertube and youtube.

v0.9.0

Fix #11

Release 0.8.0

Merge python3 test from Windows thanks to @Zykino

An upload to Peertube may be slower or have a slower encoding on the 
server.
Also why not give a preference to the open source host. As it won’t slow 
Youtube only uploads.

v0.7.1

Release v0.7.0