Sideload of models for nodes from remote yang sources repository

The system should allow for easy sideload of models for devices that do not support netconf monitoring. An operator should be able to specify in the device configuration (along with IP address and credentials) where to load the models from.

A user should be able to specify a URI for each model that the user wants to be loaded into the controller for the device. The URI can point to an http/https download, ftp download, or a local file.