Plugin be-at.tv: Schema offset can be float or int 

For the be-at.tv plugin, the offset needs to be validated as `float, int` rather than just `int`. An example of a stream which uses a float offset is: `http://www.be-at.tv/brands/o2-academy/o2-academy-brixton/hospital-we-are-18/etherwood-sp-mc`

Thanks