Material conversion enhancements

Material conversion as its current form is not useful in most scenarios. There are two enhancements that can make it work for many scenarios:

1. Allow calculation of source quantity based on the destination quantity:
   Most of the time when you have a process cell that converts a material to another one, the measurement you have in your output is not based on the material you have in the work center, the measurement is actually showing your destination quantity. So basically we need a conversion that can use the destination quantity and calculates the source quantity based on that.
   

2. Allow time as a parameter in material conversion expression:

Another enhancement that can make material conversion useful is allow the time element in the expression. Most of the time for the calculation we need to get values from a tag therefore we need to be able to get the right sample of the tag.