Use the simpler & slightly more efficient 'Map::computeIfAbsent' method
in place of the common pattern:

  map.putIfAbsent(key, newValue());
  V value = map.get();

(Clean up BondRepository + some cases missed from BurningManService.)

Replace all raw uses of 'Bond<T extends BondedAsset>', mostly with
wildcards (that is, 'Bond<?>'), to prevent compiler/IDE warnings.

Also rename the 'T extends Bond<R>' & 'R extend BondedAsset' type params
of 'BondRepository<..>' to 'B' & 'T' respectively, as this is a little
less confusing.

Fix raw usage of the following types, all of which (apart from
Comparator) touch the DAO packages somewhere:

  Comparable, Comparator, GetStateHashesResponse, NewStateHashMessage,
  RequestStateHashesHandler, PersistenceManager

(Also replace 'Integer.valueOf' with the non-boxing but otherwise
identical method 'Integer.parseInt', in the class 'TxOutputKey'.)

Fix the broken stubbing of 'PersistenceManager', which had gone stale as
a result of the conversion of 'Preferences' to asynchronous persistence
in commit 3f4d6e6 (2020/10/12). This caused the assertions in the
'readPersisted' continuation blocks of 3 of the 4 tests not to be
reached. Fix by stubbing the async 'persistenceManager::readPersisted'
method with a callback, instead of stubbing 'getPersisted'.

NOTE: Alternatively, we could add a testing-only 'readPersistedSync'
method to 'Preferences' for consistency, as this is how the other broken
(failing) tests resulting from 3f4d6e6 were fixed (in commit 68583d8).

This is in anticipation of speedups we wish to make, as JProfiler
reveals it to be a hotspot during new block arrivals (which are tricky
to profile, as they occur at random).

Alleviate a cubic time bug during the update of the bonded roles
repository, reducing it to quadratic running time. On Mainnet, this
gives a roughly ten-fold speedup and should allow better scaling in the
event that many new bonded roles are added.

Replace calls to 'BondedRolesRepository.findBondedAssetByHash' with a
lookup into a lazily initialised map of bonded assets (Roles) by hash
(reset at the start of each call to 'BondRepository.update()' to prevent
stale caching). This avoids rescanning the roles list for every pair of
roles and lockup tx outputs, thus reducing the number of steps (to
highest order) from:

  #roles * #roles * #lockup-tx-outputs

to:

  #roles * #lockup-tx-outputs

(The logs show 2 or 3 calls to 'BondedRepository.update()' every time a
new block arrives, and while this was only taking around a second or so
on Mainnet, it could potentially grow to something problematic with
cubic scaling in the number of bonded roles.)