In order to keep things simple, I've fixed this by exporting commands for
"network load file" and "network load url" to distinguish loading a
network file (SIF, XGMML, etc.) from the table loader, which uses
"network import".  This commit just exposes the existing task factories.
Fixes #2398

Change-Id: I82bb5ca9774682a622f0a5ed1cba8e1b8240ae9a