Changing last_confirmed_view behavior

[majecty]

At which view a block is finalized is important information(Verifying signatures needs the view value). Since the information couldn't be written in the block data, we should keep it in other spaces. We can query the data in two places. One is the next block's seal. Tendermint seal data contains the previous block's finalized view data. The other one is the Tendermint module's last_confirmed_view

The problem is, the Tendermint module overwrites last_confirmed_view when it enters the Commit step to the current height's finalized view. If the Tendermint module doesn't receive any proposal block at the Commit state, we can't query the previous block's finalized view anywhere.

To solve the problem, I suggest saving both previous_block_finalized_view and current_block_finalized_view in the Tendermint module.

[majecty]

Fixed by #1820