cubicweb-mediaplayer #4442384 Cleaning names [validation pending]

rename MediaMixIn into FileBytesMixIn

prioritynormal
typeenhancement
done in0.1.4
load0.200
load left0.000
closed by#dce8ac0854ba [cleaning] rename `MediaMixIn` into `FileBytesMixIn`
patch[cleaning] rename `MediaMixIn` into `FileBytesMixIn` [applied]