Support accessing old history after hard-forks

[youngjoon-lee]

Requested by korbit and other trading platforms.

Consider to

• Add a new column chain_id as the 1st primary key to all DB tables used by the explorer.
• Display the chainId on all tables in Web UI.
• Check if wallet needs to be changed. Probably, yes.

[youngjoon-lee]

As workaround,
I copied the panacea-2database to the panacea-2-txs-merged database.
And, inserted old chain transactions into the transactions table (in the panacea-2-txs-merged database).
So, old transactions can be accessible by https://wallet.medibloc.org/en/tx/{hash}:0.
It works because txhash is unique across all chains.

However, old blocks are still not accessible.

So, we need to change the entire structure, as I wrote on the issue description above.