Fix provisioning imports in tf tools.

[riga]

This PR fixes some imports in the tensorflow tools.

Last time, we forgot to expose the deprecated load_graph and save_graph functions (that we renamed to load_frozen_graph and save_frozen_graph, respectively). This currently results in, e.g.,

cmsml.tensorflow.save_graph(...)

not being accessible at all whereas we just wanted to deprecate them. This "hard cut" could lead to some complications downstream.

For consistency, a new release could be necessary.