feat: abort collaborative transaction

[theborakompanioni]

Closes #269.

Adds the ability to abort a running taker operation.

How to test

1. Send a collaborative transaction
2. Try to abort the transaction
3. Verify that the transaction was aborted and not broadcasted

You might want to watch the logs while testing this feature with npm run regtest:logs:jmwalletd

Question: Currently, the text only says "Are you sure you want to abort the collaborative transaction?"..
Stopping a taker operation might lead to end up wasting a "retry" (when commitment was already sourced).. Should it mention that it might lead to inconveniences if this is used "too much in a row"? How to communicate this best?

[dergigi]

Question: Currently, the text only says "Are you sure you want to abort the collaborative transaction?"..
Stopping a taker operation might lead to end up wasting a "retry" (when commitment was already sourced).. Should it mention that it might lead to inconveniences if this is used "too much in a row"? How to communicate this best?

Let's leave it as is and see how many users run into these kinds of issues in the wild.

[dergigi]

Looks good to me, tACK ✅

[dergigi]

Notes to self:

• "Abort" sounds quite drastic, maybe reword to "Cancel"?
• "Collaborative transaction started" toast seems unnecessary now; remove?