pep8
remove variable not used.
Add the opt tag name inplace_elemwise_optimizer to inplace_opt as this
is the variable name used.

I lost 1h before undersanding it isn't the name used in the optdb.

Also test that we can disable inplace and fusion opt with MonitorMode.
Extend doc of MonitorMode.
Add opt that lift flatten toward the inputs for unary elemwise.

This enable elemwise opt with flatten in the middle.
This can also enable more elemwise fusion that got split by flatten.