Common code between verify and blocks

Following #262 (closed)

Tasks

• common function to gather a range of blocks specifying from_, and to.
• common test on this function gathering blocks on a range by chunks
• two modes for blocks explorer:
  • current: specify number of blocks from head, 0 default to current window
  • Same as verify: a range of blocks: blocks number from an to.
  • How to specify/filter the two modes: --range, --from-head/--head (this one would be the default).

This could be a method into a class that would inherit the @click.command decorator. Would that work?

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Later

• command blocks with sub-commands explorer, verify, …: is this possible with Click?