Fix edge creation between graph nodes #107
Description
The current implementation of Phlex forms edges based on product names only, although the product names can be qualified with a module name (i.e. the 'M' and 'N' keys specified in #106). There is currently no checking that the types are consistent between one node's output port and another node's input port. In addition, a user cannot specify a creator name to indicate that an algorithm should consume a data product produced by that creator—instead, the user must give an explicit product name.
This is the top-level PR for reconciling these two issues.