Deriving dep info from fetched artifact instead of rebar.config.

This change will allow the plugin to handle second order dependencies without recreating rebar's dependency resolution.

Example (direct dependency):
dev3 writes dep1 depending on dep from github.com/dev1/dep
dev4 writes dep2 depending on dep from github.com/dev2/dep

Example (indirect dependency):
dev5 writes depdep1 depending on dep1 from github.com/dev3/
dev6 writes depdep2 depending on dep2 from github.com/dev4/

Depending on order in rebar.config, possible to incorrectly derive remote.  If depdep1 is first, dep's remote will be from dev1.  If depdep2 is first, dep's remote will be from dev2.  However, at no point in the top level rebar.config is dep's remote explicitly stated.