Mark mature coinbase deposits as immature following tip rollback

[jp1ac4]

This relates to the following TODO:

liana/lianad/src/database/sqlite/mod.rs

Line 801 in e246305

// TODO: mark coinbase deposits that were mature and became immature as such.

Now that we save transactions in the DB, we could check if a coin is from a coinbase deposit and should be marked as immature following a tip rollback. For this, I think it would be required to add an is_coinbase column to the transactions table.

The effect of this issue is that an immature coin might not be marked as such following a reorg and could therefore be included in a draft spend, even though it would be unspendable until mature.