some routing updates

each side of a network change updates seperatialy (no recursion through
_prevAdjacentRouter)

_prevAdjacentRouter isn't needed. and is removed

tidy up the actor class.

getConnectedPowerProvider isn't used anywhere, and is removed (power
node searching moved to PathFinder, as it is looking at all the tiles
directly, anyway)

_powerAdjacent is now null if there is no powerAdjacent (lsa.power is
potentially null now also, checks added)