Updated example genesis.json configuration section, added londonBlock within config.

The `README.md` links the Gitter channel for discussions, but the
official docs and even the Gitter channel itself recommend using the
official Discord Server for such discussions.
This PR simply changes the Gitter link and provides Discord invite link.

This removes support for all deprecated flags except --rpc*.

The legacy dot-org URL was displaying a message about the repository
having migrated to the dot-com service, which now covers open-source
projects as well.

* cmd/utils: make goerli the default testnet

* cmd/geth: explicitly rename testnet to ropsten

* core: explicitly rename testnet to ropsten

* params: explicitly rename testnet to ropsten

* cmd: explicitly rename testnet to ropsten

* miner: explicitly rename testnet to ropsten

* mobile: allow for returning the goerli spec

* tests: explicitly rename testnet to ropsten

* docs: update readme to reflect changes to the default testnet

* mobile: allow for configuring goerli and rinkeby nodes

* cmd/geth: revert --testnet back to ropsten and mark as legacy

* cmd/util: mark --testnet flag as deprecated

* docs: update readme to properly reflect the 3 testnets

* cmd/utils: add an explicit deprecation warning on startup

* cmd/utils: swap goerli and ropsten in usage

* cmd/geth: swap goerli and ropsten in usage

* cmd/geth: if running a known preset, log it for convenience

* docs: improve readme on usage of ropsten's testnet datadir

* cmd/utils: check if legacy `testnet` datadir exists for ropsten

* cmd/geth: check for legacy testnet path in console command

* cmd/geth: use switch statement for complex conditions in main

* cmd/geth: move known preset log statement to the very top

* cmd/utils: create new ropsten configurations in the ropsten datadir

* cmd/utils: makedatadir should check for existing testnet dir

* cmd/geth: add legacy testnet flag to the copy db command

* cmd/geth: add legacy testnet flag to the inspect command

* add istanbul and muirGlacier to genesis states in README

* remove muirGlacier, relocate istanbul

* Accounts in alloc field must already exist

Note that accounts in alloc field must already exist, as pointed out by Simeon Vanov in https://gettoshare.com/2017/10/30/how-to-use-genesis-json-alloc-property/

* Change wording per PR review comment

* README: minor fixups

* Change chainId in genesis block to 8888 from 0 

Change chainId in genesis block to 8888 from 0 per Moriteru in https://ethereum.stackexchange.com/a/28082/40230.

* Replace 8888 with “<arbitrary positive integer>”

Per PR review, replace Moriteru’s arbitrary positive integer 8888 with “<arbitrary positive integer>” in chainId field.

Changed http:// to https:// on JSON-RPC link in README.md

Signed-off-by: YaoZengzeng <yaozengzeng@zju.edu.cn>

* eth: added travis build status for master branch

* README: fix travis badge order, link to CI

* README: add goreportcard.com badge to Readme

* README: fix double github.com

* Remove --fast flag and clarify default

`--fast` is no longer a flag it's `--syncmode "fast"` and that is the default

* Remove --cache flag

--cache=512 is no longer required as of 1.8 as the default has been increased

* README: Minor cache amount fix, mention Rinkeby

missing period at line 119