[1.0.1 -> main] Should never move from a signed_block in a shared_ptr

[heifner]

Should never move a signed_block that could still be used. The point of shared_ptr is shared data, you don't know if being used by something else unless you just created it. For example if still in the forkdb. Would have preferred to delete the move constructor and move operator= but unfortunately those are needed for our unused http push_block.

Merges release/1.0 into main including #738

Resolves #737

[ericpassmore]

Note:start
category: Other
component: Plugins/Cleos/Utils
summary: Do not move a signed block that may be used later.
Note:end