channeldb: add new NoFundingTxBit modifier to ChannelType
channeldb: add new NoFundingTxBit modifier to ChannelType

In this commit, we add a new bit to the existing ChannelType bitfield.
If this bit is set, then it signals that we have the funding transaction
stored on disk. A future change will enable lnd to have the funding
transaction be constructed externally, allowing for things like funding
from a hardware wallet, or a channel created as a sub-branch within an
existing channel factory.

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