This commit changes the logic when garbage collecting forwarding
packages such that they are removed once when the function is called,
and then again upon subsequent ticks. This allows us to bump the
peer timer to 1 hour to limit the number of db transactions happening
in lnd. The forwarding packages need to be removed initially as
otherwise a flappy node will never have them garbage collected.
In this commit, we split the database storage into two classes: remote
and local data. If etcd isn't active, then everything is actually just
local though we use two pointers everywhere. If etcd is active, then
everything but the graph goes into the remote database.
