Update on-chain balance immediately after channel closure

[luckysori]

Fixes #461.

The coins are correctly moved to a pending state, like we do with any other on-chain transaction.

The user is also informed about what to expect when closing the channel.

It's important to note that if the user runs into a force-closure for some other reason, the coins will also go into a pending state and be reflected in the overall on-chain balance, but it will take hundreds of confirmations for the coins to be confirmed.

[luckysori]

bors r+

[bors[bot]]

Build succeeded:

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