feature request: implement fee tiers

[artikozel]

At the moment any person requesting liquidity from the LP pays a set fee regardless of the channel size. If the Decred LN and services using it really take off the demand for liquidity is bound to go up. If that happens and the liquidity providers adjust the max channel sizes users are able to request they'll have to adjust the fee sizes in order to compensate for the lockup of larger and larger sums of DCR, but without tiered fees a person requesting 0.1 DCR will have to pay the same (higher) fee as a person requesting 10 DCR or 50 DCR.
I'm wondering if tiered fees are a viable solution (in terms of implementation) or if there's already a solution being cooked up to account for a possible scenario like the one above.