Rates for composite transients apply to each template

[mginolin]

When using composite/collection of transients (e.g. non Ias), the rate that is passed to from_draw() is applied to each of the template individually and not the collection of templates. Below is an example in which in order to get the same number of SNe for different SN types you have to normalise the rate by the number of templates. This might not be an issue for collections of transients but it is not the most logical option for composite transients.