refactored to allow clean shutdowns on SIGINT

includes following commits by Michalis
* Move btcwallet kill, receive from spendAfter in a select
* Declutter logs and split actor into different goroutines
IMPORT PATH MODIFICATION CHANGESET
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Please use this changeset as the first one on top of the conformal codebase.
Note that if there are new imports, they need to be changed as part of this
changeset. In general, use "git rebase" on github.com/conformal's version
and apply this changeset first.