all: integrate the freezer with fast sync

* all: freezer style syncing

core, eth, les, light: clean up freezer relative APIs

core, eth, les, trie, ethdb, light: clean a bit

core, eth, les, light: add unit tests

core, light: rewrite setHead function

core, eth: fix downloader unit tests

core: add receipt chain insertion test

core: use constant instead of hardcoding table name

core: fix rollback

core: fix setHead

core/rawdb: remove canonical block first and then iterate side chain

core/rawdb, ethdb: add hasAncient interface

eth/downloader: calculate ancient limit via cht first

core, eth, ethdb: lots of fixes

* eth/downloader: print ancient disable log only for fast sync

light/trie.go

@@ -141,7 +141,7 @@ func (t *odrTrie) GetKey(sha []byte) []byte {
 	return nil
 }
 
-func (t *odrTrie) Prove(key []byte, fromLevel uint, proofDb ethdb.Writer) error {
+func (t *odrTrie) Prove(key []byte, fromLevel uint, proofDb ethdb.KeyValueWriter) error {
 	return errors.New("not implemented, needs client/server interface split")
 }