neutrino: configure UtxoScanner start/stop
neutrino: configure UtxoScanner start/stop

This commit moves the Start and Stop calls to the
UtxoScanner so that they are consistent with the
life-cycle of the ChainService. It also changes the
instantiation of the UtxoScanner so that it uses the
new UtxoScannerConfig.

lightninglabs/neutrino