* cmd, core, eth, light, trie: disable recording preimage by default

* core, eth: fix unit tests

* core: fix import

* all: change to nopreimage

* cmd, core, eth, trie: use cache.preimages flag

* cmd: enable preimages for archive node

* cmd/utils, trie: simplify preimage tracking a bit

* core: fix linter

Co-authored-by: Péter Szilágyi <peterke@gmail.com>

* cmd, core, eth, light, trie: dump clean cache periodically

* eth: update config

* trie: minor fix

* core, trie: address comments

* eth: remove useless

* trie: print clean cache dump start too

Co-authored-by: Péter Szilágyi <peterke@gmail.com>

This change introduces garbage collection for the light client. Historical
chain data is deleted periodically. If you want to disable the GC, use
the --light.nopruning flag.

* les: loose restriction of unit tests

* les: update unit tests

* les, light: slim the unit tests

les: handler separation

This PR enables the indexers to work in light client mode by
downloading a part of these tries (the Merkle proofs of the last
values of the last known section) in order to be able to add new
values and recalculate subsequent hashes. It also adds CHT data to
NodeInfo.

* les, light: fix CHT trie retrievals

* les, light: minor polishes, test remote CHT retrievals

* les, light: deterministic nodeset rlp, bloombits test skeleton

* les: add an event emission to the les bloombits test

* les: drop dead tester code

This commit reduces database I/O by not writing every state trie to disk.

* core, light: fix chain indexer bug

* light: add new CHT

This PR implements the new LES protocol version extensions:

* new and more efficient Merkle proofs reply format (when replying to
  a multiple Merkle proofs request, we just send a single set of trie
  nodes containing all necessary nodes)
* BBT (BloomBitsTrie) works similarly to the existing CHT and contains
  the bloombits search data to speed up log searches
* GetTxStatusMsg returns the inclusion position or the
  pending/queued/unknown state of a transaction referenced by hash
* an optional signature of new block data (number/hash/td) can be
  included in AnnounceMsg to provide an option for "very light
  clients" (mobile/embedded devices) to skip expensive Ethash check
  and accept multiple signatures of somewhat trusted servers (still a
  lot better than trusting a single server completely and retrieving
  everything through RPC). The new client mode is not implemented in
  this PR, just the protocol extension.