signal: catch all termination signals by default
signal: catch all termination signals by default

In this commit, we modify the primary `signal` package to instead catch
all signals. Before this commit, it would only catch the interrupt
signal sent from the kernel. With this new commit, we'll now also catch
(or attempt to catch): `SIGABRT`, `SIGTERM`, `SIGSTOP`, and `SIGQUIT`.

LightningNetwork/lnd,LightningNetwork/lnd,aakselrod/lnd,aakselrod/lnd