SP return const random representation on empty input & SP anomaly

[breznak]

Problem: empty SP output on low overlap

Currently, when the overlap with input (unexpected input, unlearned, ..?) is too low, SP returns 0 active columns.
This causes problems in TM, and Anomaly

Proposal

I want to change SP such that

• aways returns numDesired (keeping sparsity) outputs, see SP: remove numActiveColumnsPerInhArea #549 , and this issue for cases with low overlap.
• if overlap is too low:
  • detect spatial anomaly!
    • implement the same way is TM.anomaly, used in NAB for example.
  • return a const, random SDR that designates "none, or unrecognized input"
  • may call bumpUpWeakColumns to have some imput.

This should be tested on anomaly datasets, so ideally once #205

[breznak]

Related #463