Differentiate between coop close and force-close in `Balance`

[TheBlueMatt]

There is no way to tell whether a Balance is for a coop close or an HTLC or a force-close. We should expose that info.

[moneyball]

119 worthy?

[Jasonvdb]

Would be interested in using this in Bitkit

[dunxen]

I can pick this up tomorrow. I'm not sure it would get in by 124 with some of the other work in progress but will make an attempt 👍

[TheBlueMatt]

Oh, we may want to just slip this, really we want to expose a lot more info, ala #2618 but I haven't had the time to work on #2618 :(. If you want to pick that up, that'd be huge! It was mostly there just needed tests, which were quite nontrivial....