Multiple improvements

[feelancer21]

I added multiple improvements to charge-lnd. Below a summary of the commits. Feel free to test, comment or merge.

Fixes also #111, #83 and #2

Functional Improvements

• Rules based on pending htlcs

  We include rules based on either the number of pending HTLCs or the
  next expiry.

• Introducing: inbound_level_ppm and min_inbound_fee_ppm_delta

  1. min_inbound_fee_ppm_delta is the necessary minimum change in the
     inbound_fee_ppm. The parameter uses min_fee_ppm_delta as the default.
  2. We also ensure that the inbound fee rates are only changed if the
     change is sufficiently large.
  3. If inbound_level_ppm is set, inbound_fee_ppm is calculated
     with min(inbound_level_ppm - fee_ppm; 0).

• Consideration of the local constraints during channel update

  Local constraints are used to floor/cap the min_htlc_mat/max_htlc_msat.

• Consideration of the commit fee in the balance calculation

  We take the commit fee into account when calculating the local balance
  and the remote balance, depending on who opened the channel. This
  stabilizes the calculation of balances and ratios in times of volatile
  onchain fees.

• Consideration of the unsettled balance

  We add the amounts of pending htlcs to the local and remote balance of
  a channel. Incoming htlcs are added to the remote balance and outgoing
  htlcs to the local balance.

• Add an onchain matcher

  The onchain matcher offers the possibility to enforce policies
  depending on the current onchain fees. The confirmation target
  can be configured by the user (default: 6).

• Circuitbreaker support

  It is now possible to control the node limits of a circuitbreaker
  instance dynamically.

Logging

• Printing RpcErrors and UpdateFailures

• Very verbose mode

  In this new mode we print more information than in verbose mode.
  Every matched policy is printed. That can be useful if one use a
  config with many non final policies.

Others

• Matchers are now only called once

  Until now, it could happen with several attributes that the matcher
  for a namespace was called several times unnecessarily.

• use onchain fee estimate of lnd instead of electrum

  We are using the onchain fee estimator of lnd now. Internally, lnd uses
  either bitcoind or a fee url for the estimation.

• Cleanup unused module imports

[feelancer21]

Rebased because of #116

[accumulator]

huge improvements @feelancer21, thanks!