Allow multiple --ens-api flags to be specified with value format
[tld:][contract-addr@]url.

Backward compatibility with only one --ens-api flag and --ens-addr
flag is preserved and conflict cases are handled:

 - multiple --ens-api with --ens-addr returns an error

 - single --ens-api with contract address and --ens-addr with
   different contract address returns an error

Previously implemented --ens-endpoint is removed. Its functionality
is replaced with multiple --ens-api flags.

Implement a CLI flag that can be repeated to allow multiple ENS
resolvers for different TLDs.

* cmd, dashboard: dashboard using React, Material-UI, Recharts

* cmd, dashboard, metrics: initial proof of concept dashboard

* dashboard: delete blobs

* dashboard: gofmt -s -w .

* dashboard: minor text and code polishes

* cmd/puppeth: handle encrypted ssh keys

* cmd/puppeth: fix unconvert linter error

* build: enable unconvert linter

 - fixes #15453
 - update code base for failing cases

* cmd/puppeth: replace syscall.Stdin with os.Stdin.Fd() for unconvert linter

* cmd, consensus, core, miner: instatx clique for --dev

* cmd, consensus, clique: support configurable --dev block times

* cmd, core: allow --dev to use persistent storage too

This commit introduces a network simulation framework which
can be used to run simulated networks of devp2p nodes. The
intention is to use this for testing protocols, performing
benchmarks and visualising emergent network behaviour.

* ethdb: add Putter interface and Has method

* ethdb: improve docs and add IdealBatchSize

* ethdb: remove memory batch lock

Batches are not safe for concurrent use.

* core: use ethdb.Putter for Write* functions

This covers the easy cases.

* core/state: simplify StateSync

* trie: optimize local node check

* ethdb: add ValueSize to Batch

* core: optimize HasHeader check

This avoids one random database read get the block number. For many uses
of HasHeader, the expectation is that it's actually there. Using Has
avoids a load + decode of the value.

* core: write fast sync block data in batches

Collect writes into batches up to the ideal size instead of issuing many
small, concurrent writes.

* eth/downloader: commit larger state batches

Collect nodes into a batch up to the ideal size instead of committing
whenever a node is received.

* core: optimize HasBlock check

This avoids a random database read to get the number.

* core: use numberCache in HasHeader

numberCache has higher capacity, increasing the odds of finding the
header without a database lookup.

* core: write imported block data using a batch

Restore batch writes of state and add blocks, tx entries, receipts to
the same batch. The change also simplifies the miner.

This commit also removes posting of logs when a forked block is imported.

* core: fix DB write error handling

* ethdb: use RLock for Has

* core: fix HasBlock comment

* cmd/evm: adds ability to run individual state test file

* cmd/evm: Fix statetest runner to be more json friendly

* cmd/evm, tests: minor polishes, dump state on fail

* cmd/evm, core/vm, internal/ethapi: Add 'err' to tracer interface CaptureEnd

* cmd/evm: fix nullpointer when there is no error

* cmd: fix megacheck warnings

* cmd: revert time.Until changes, keep readFloat

Previously, NewManifest was asynchronous so subsequent code which tried
to use the returned manifest could error as the manifest was not yet
persisted.

* core: reduce txpool event loop goroutines and sync structs

* cmd, core, eth: journal local transactions to disk

* core: journal replacement pending transactions too

* core: separate transaction journal from pool