Removed from as a requirement and changed

Removed the from as a requiremet from the RPC eth_call. Xeth#Call now
also default values to:

1. Supplied account
2. First account if any
3. No managed account => 000000..00

rpc/args.go

@@ -279,11 +279,6 @@ func (args *CallArgs) UnmarshalJSON(b []byte) (err error) {
 		return NewDecodeParamError(err.Error())
 	}
 
-	if len(ext.From) == 0 {
-		return NewValidationError("from", "is required")
-	}
-	args.From = ext.From
-
 	if len(ext.To) == 0 {
 		return NewValidationError("to", "is required")
 	}