core+gui+cli: network-fee invalidation, will-tree fixes, i18n refresh

- #64: the on-chain invalidation now pays the current network fee through a
  configurable fee-policy setting (default eta:2); baltx_fees is only the
  offline fallback. The change output is dust-guarded: coins are appended until
  the change clears the wallet dust threshold.
- #65: a will item whose father is missing/stale is handled defensively in
  check_invalidated and discarded by add_willtree instead of raising KeyError.
- #66: children are stored as a list (dict accepted for older data/tests).
- Refresh the translation catalogs and fix stale source line references.
- New tests for the invalidation fee policy, the dust guard and the father
  link handling.

bal/cli/controller.py

@@ -417,6 +417,7 @@ class BalController:
             will_locktime=Will.get_min_locktime(
                 willitems, default_value=self.date_to_check
             ),
+            fee_policy_descriptor=self.plugin.INVALIDATION_FEE_POLICY.get(),
         )
         if tx is not None:
             try: