Register `ApplyAlpha` layer templates
Created by: thesps
As first noticed by @jmitrevs in #490, since the merge of #395 the ApplyAlpha
layer is no longer written out. The issue was that the templates weren't registered, so I've added that here. I cherry picked the commit adding the test that @jmitrevs added to expose the problem. It fails on current master, passes on the PR.
I started a quantized_templates.py
module anticipating that we may add more specialized functions / layers for handling scale factors etc for the QONNX work later, so their template registration might go there.