This commit adds a new struct, `HarnessNode`, to manage the lnd process
used in our itest. This struct is built upon `HarnessRPC`, `State`, and
`NodeWatcher`.
This commit adds a new struct, `nodeWatcher`, to keep track of all graph
topology updates of a given node, including updates from channel edges,
policies, and peers.
This commit adds a new package `lntemp/node` and inside it a new struct
`State` is added to track the internal node state. This enables us using
the same running nodes accross tests without wrong uncleaned states.
