swarm: creates Swarm landing page for browser 'localhost:xxxx/' GET request when running Swarm (#15926)

* swarm: began work on GetHandleFile method re: issue #155

* swarm: now able to serve landing page template

* swarm: added landing page template

* swarm: landing page has working input

* swarm: fixed CSS issue in template

* swarm: deleted extra lines

* swarm: deleted time header and made redirect a relative path

* swarm: removed code mistakenly left

whisper: filters no longer get removed after a while

* swarm: initial instrumentation with go-metrics

* swarm: initialise metrics collection and add ResettingTimer to HTTP requests

* swarm: update metrics flags names. remove redundant Timer.

* swarm: rename method for periodically updating gauges

* swarm: finalise metrics after feedback

* swarm/network: always init kad metrics containers

* swarm/network: off-by-one index in metrics containers

* swarm, metrics: resolved conflicts

Without this, deprecated bzzr requests just return an empty response.

Signed-off-by: Lewis Marshall <lewis@lmars.net>

whisper: light client mode introduced

* core: flush out trie cache more meaningfully on stop

* core: upgrade legacy tests to chain maker

Fix race condition in whisperv6/peer.go

* core, vm, common: define constantinople fork, start implementation of shift instructions

* vm: more testcases

* vm: add tests for intpool erroneous intpool handling

* core, vm, common: fix constantinople review concerns

* vm: add string<->op definitions for new opcodes

* go-metrics: fork library and introduce ResettingTimer and InfluxDB reporter.

* vendor: change nonsense/go-metrics to ethersphere/go-metrics

* go-metrics: add tests. move ResettingTimer logic from reporter to type.

* all, metrics: pull in metrics package in go-ethereum

* metrics/test: make sure metrics are enabled for tests

* metrics: apply gosimple rules

* metrics/exp, internal/debug: init expvar endpoint when starting pprof server

* internal/debug: tiny comment formatting fix

eth, les, light: filter on logs only, derive receipts on demand

swarm: repeated --ens-api CLI flag (#14386)

* p2p: remove unused code

* p2p: remove unused imports

RPC Server readRequest method sets the serverRequest error service
value as the rpcRequest.method and this change sets it to the right
service value.

core: yeah, funny file, drop it

p2p/protocols, p2p/testing: protocol abstraction and testing

cmd/faucet: resolve twitter user from final redirect

cmd/puppeth: Don't allow hyphen in network name. Fixes #16155

accounts/abi: Fix the bug of mobile framework crashing

accounts/abi: add another unpack interface

* ethapi: prevent creating contract if no data is provided

* internal/ethapi: downcase error for no data on contract creation

This change removes a peer information from dialing history
when peer is removed from static list. It allows to force a
server to re-dial concrete peer if it is needed.

In our case we are running geth node on mobile devices, and
it is common for a network connection to flap on mobile.
Almost every time it flaps or network connection is changed
from cellular to wifi peers are disconnected with read
timeout. And usually it takes 30 seconds (default expiration
timeout) to recover connection with static peers after
connectivity is restored.

This change allows us to reconnect with peers almost
immediately and it seems harmless enough.

cmd, console: support all termination signals