Rather than have specific-purpose levels, have an array of
[blockcount, feerate], and rebuild the specific-purpose levels
for now on top.
We also keep a *separate* smoothed feerate, so you can ask for that
explicitly.
Since all the plugins used the same formula to derive the different
named fee levels, we apply the reverse to return to the underlying
estimates: updating the interface comes next.
This is ugly for now, but various specific-purpose levels will be
going away, as we shift to deadline-driven fees.
This temporarily breaks the floor calculation, so that test is
disabled.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
cdb85d5618