Automated Action Delay Due to Block Size

[youkaicountry]

If an automated action would overrun the block size, it should be delayed.

AC:

• Action delay during block generation
• Action delay during block validation
• Cleanup of delayed optional actions

[mvandeberg]

Action delay in block generation is already implemented. Action delay in block validation is still needed.

[mvandeberg]

Cleaning up optional actions is needed and will be implemented in this issue.

[mvandeberg]

Cleaning up expiration was already implemented and updated in #2718

steem/libraries/chain/database.cpp

Lines 3480 to 3491 in 90ff402

	// Clear out "expired" optional_actions. If the block when an optional action was generated
	// has become irreversible then a super majority of witnesses have chosen to not include it
	// and it is safe to delete.
	const auto& pending_action_idx = get_index< pending_optional_action_index, by_execution >();
	auto pending_itr = pending_action_idx.begin();
	auto lib_time = fetch_block_by_number( get_dynamic_global_properties().last_irreversible_block_num )->timestamp;
	while( pending_itr != pending_action_idx.end() && pending_itr->execution_time <= lib_time )
	{
	remove( *pending_itr );
	pending_itr = pending_action_idx.begin();
	}