Miner race fixes

les, p2p/discv5: implement server pool, improve peer selection, light fetcher and topic searching

netstats: time and block history

NSIS has a default MAX_STR_LEN of 1024. If $ENV{PATH} is longer
the returned string is truncated to an empty string. Its then not
possible to distinguis between the variable not set or too long.
As a result the variable is set with the location where geth and/or
dev tools are installed. This may override any previous set values.

The transaction pool keeps track of the current nonce in its local pendingState. When a
new block comes in the pendingState is reset. During the reset it fetches multiple times
the current state through the use of the currentState callback. When a second block comes
in during the reset its possible that the state changes during the reset. If that block
holds transactions that are currently in the pool the local pendingState that is used to
determine nonces can get out of sync.

* build: modify the iOS namespace to iGeth (gomobile limitation)
* mobile: assign names to return types for ObjC wrapper
* mobile: use more expanded names for iOS/Swift API

Environment is now a struct (not an interface). This
reduces a lot of tech-debt throughout the codebase where a virtual
machine environment had to be implemented in order to test or run it.

The new environment is suitable to be used en the json tests, core
consensus and light client.

eth/filters, ethclient, ethereum: API improvements

This field used to be assigned by the filter system and returned through
the RPC API. Now that we have a Go client that uses the underlying type,
the field needs to move. It is now assigned to true when the RemovedLogs
event is generated so the filter system doesn't need to care about the
field at all.

While here, remove the log list from ChainSideEvent. There are no users
of this field right now and any potential users could subscribe to
RemovedLogsEvent instead.

ethclient now returns ethereum.NotFound if the server returns null and
no error while accessing blockchain data.

The light client cannot provide arbitrary transactions. The change to
split transaction access into its own interface emphasizes that
transactions should not be relied on and recommends use of logs.

It should never return null for a known uncle, but even if it does
we can't just crash.

* Filter refactoring
* API tests added + bugfix
* fixed the error logs
* FilterID fixed
* test cases fixed
* key generation updated
* POW updated
* got rid of redundant stuff

ethstats: check if received event is valid

cmd/geth: tidied up the source

ethstats: don't drop concurrent head reports (mini forks)

node: improve error handling for web3_sha3 RPC method

* miner: removed unnecessary state.Copy()

* eth: made use of new miner method without state copying

* miner: More documentation about new method

cmd: drop DAO related choice flags since ETC diverged

ethstats: report block miner, gas limit and gas consumption