Web3 rework + misc fixes.

[hackmod]

• [x] restore accidentally removed web3 batch-job code to make it work as intended.
  • without batch job, geth/multi-geth does not work as intended.

(please see commit 899b5ff6c4)

• restore various accidentally removed features
  • [x] restore customCss (accidentally removed by commit f281d915)
  • [x] restore showRichList option
  • [x] use web3 2.0.0-alpha.1
  • [x] replace the outdated web3-explorer with the new web3 2.x method.

Notes

• low-level batch job method only works with the web3 up to version 1.2.1.
• websocket seems not stable enough

[hackmod]

web3 1.2.1 websocket seems not stable enough

<--- Last few GCs --->

[16217:0x3d4a070]  3372700 ms: Mark-sweep 2343.8 (2624.6) -> 2343.6 (2624.6) MB, 3307.0 / 0.0 ms  allocation failure GC in old space requested
[16217:0x3d4a070]  3376665 ms: Mark-sweep 2343.6 (2624.6) -> 2343.5 (2583.6) MB, 3964.2 / 0.0 ms  last resort GC in old space requested
[16217:0x3d4a070]  3379630 ms: Mark-sweep 2343.5 (2583.6) -> 2343.5 (2576.6) MB, 2964.0 / 0.0 ms  last resort GC in old space requested

<--- JS stacktrace --->

==== JS stack trace =========================================

Security context: 0x2d448b125891 <JSObject>
    1: _addResponseCallback [/home/explorer/node_modules/web3-providers-ws/src/index.js:~227] [pc=0x4540f7790f1](this=0x2b41c11cec1 <WebsocketProvider map = 0xdf48485d5e9>,payload=0x1fd4ec1d45e1 <Object
 map = 0xdf48484e1d9>,callback=0x1fd4ec1d4619 <JSFunction (sfi = 0xf2e565027d9)>)
    2: send [/home/explorer/node_modules/web3-providers-ws...

FATAL ERROR: CALL_AND_RETRY_LAST Allocation failed - JavaScript heap out of memory
...

[kimisan]

@hackmod may you check the continuous-integration/travis-ci/pr ?

[hackmod]

@kimisan // node version issue resolved. ready to merge now!

[hackmod]

travis-ci passed at https://travis-ci.org/EthersocialNetwork/explorer/builds/625344321

[kimisan]

@phyro @realcodywburns Can you help to merge the pull request. Thanks

[realcodywburns]

Merging w/o travis ci test run.need to troubleshoot ci/cd pipeline. Code passed in abo e mentioned tests