Change outputs should be omitted from review

[ImplOfAnImpl]

Change outputs should be detected and then either:

• completely omitted from the review;
• or just marked as change.

Edit: since #23 change outputs are already recognized and marked as such. So now this issue is about omitting them from review when possible.

There are 2 TODOs related to this - one in TxProcessingContext::show_spinner and one near TxOutputData.