looper step settings are not mode specific; Run and Step should be 2 distinct modes

[rcoreilly]

• If you single step training at the epoch level, it fails to run the testall
• testall Run() should run regardless of any existing stepping -- Run() should mean run without stepping, and Step() should mean step..
• ergo, stepping settings should be stored at the Stack level, not the global manager, and should be cleared for selected mode when starting a Run()
• Run() should also take the mode to select the appropriate stack -- too error-prone having it depend on latent state.

I will take this and add appropriate test cases and also verify in my IRL test.

[rcoreilly]

Fixed by f46807a -- still needs test but main use test works.