Add optionalized multistage module, add linear incrementing stage

[Purg]

What does this PR do?

Add a version of the multistage module that can do a few additional optional things, otherwise it should allow the same functionality of the existing multistage module.

• Allow optional use of a single stage that linearly increases dilation value.
• Allow optional use of a single stage that is set to a constant dilation value.
  • This can be set to 1 to effectively disable dilation.
• Allow optional usage of softmax going into single stage layers (defaulted to False)
• Allow optional addition of previous single stage logit outputs to successive single stage logit outputs.

Added new experiment config for M2 to make use of this new model, linear single stages, no internal softmaxing and residual single stage combination.