Prevent relay of invalid IPs, add --netrestrict

common/registrar, eth: removed registrar (tech debt)

Makefile, build: do proper mobile builds, not cross builds

The registrar was broken, unmaintained and there is a much better
replacement: ENS.

(cherry picked from commit 6ca8f57b08d550613175260cab7633adcacbe6ab)

(cherry picked from commit d54ad55c6079ae6eab93d7f34ce5c4ec829f8e5b)

core, core/state: fixed consensus issue added touch revert

Implemented proper touch revert journal entries and copied a Parity
consensus bug in order to remain in sync with the current longest chain.

miner: remove dead code, add gas price getter

core: remove dead event

build, internal/build: simplify unstable build checks

I didn't add this initially because the command I tried was too slow.
The 'git for-each-ref ...' invocation takes 40ms on my machine. That
ought to be acceptable.

build: remove hash metadata from cocoapod version

All account's nonce start at 0.

The p2p packages can now be configured to restrict all communication to
a certain subset of IP networks. This feature is meant to be used for
private networks.

The discovery DHT contains a number of hosts with LAN and loopback IPs.
These get relayed because some implementations do not perform any checks
on the IP.

go-ethereum already prevented relay in most cases because it verifies
that the host actually exists before adding it to the local table. But
this verification causes other issues. We have received several reports
where people's VPSs got shut down by hosting providers because sending
packets to random LAN hosts is indistinguishable from a slow port scan.

The new check prevents sending random packets to LAN by discarding LAN
IPs sent by Internet hosts (and loopback IPs from LAN and Internet
hosts). The new check also blacklists almost all currently registered
special-purpose networks assigned by IANA to avoid inciting random
responses from services in the LAN.

As another precaution against abuse of the DHT, ports below 1024 are now
considered invalid.

The new package contains three things for now:

- IP network list parsing and matching
- The WSAEMSGSIZE workaround, which is duplicated in p2p/discover and
  p2p/discv5.

* build: use metatags on cocoapods, not prerelease tags
* build: fix Maven and CocoaPods author email addresses

This simplifies the build and should speed it up a bit because the
standard library doesn't need to be cross compiled on the 32bit builder.

Changed http:// to https:// on one link in README.md

ci.go decides whether a build is unstable by looking at the branch and
tag. This causes issues when a GitHub release is created on the master
branch because the build is considered unstable (the CI environment
reports the branch as "master").

Fix this by looking at the tag only. Any tagged build is stable.