Add minimal unlock block height in popup of nervos dao

[Keith-CY]

Visit https://explorer.nervos.org/nervosdao

When the icon of safe deposit box in a withdraw_phrase_1 transaction is hovered, the popup shows as follows.

It includes

• Deposit capacity
• Compensation to be issued
• Compensation period
• Compensation time

Along with the withdraw_phrase_1 performed, the timing of unlock is determined and can be prompted in the popup.

As mentioned at https://github.com/nervosnetwork/rfcs/blob/master/rfcs/0023-dao-deposit-withdraw/0023-dao-deposit-withdraw.md#withdraw-phase-2

When the asset is deposited at block_a, and withdrawn at block_b, the minimal block number, block_c, to unlock conforms to

n = Math.ceil((block_b - block_a)/180)
block_c = block_a + 180 * n

By doing so, users are indicated when to perform the withdraw_phrase_2 on the Explorer.