* rpc: implement websockets with github.com/gorilla/websocket

This change makes package rpc use the github.com/gorilla/websocket
package for WebSockets instead of golang.org/x/net/websocket. The new
library is more robust and supports all WebSocket features including
continuation frames.

There are new tests for two issues with the previously-used library:

  - TestWebsocketClientPing checks handling of Ping frames.
  - TestWebsocketLargeCall checks whether the request size limit is
    applied correctly.

* rpc: raise HTTP/WebSocket request size limit to 5MB

* rpc: remove default origin for client connections

The client used to put the local hostname into the Origin header because
the server wanted an origin to accept the connection, but that's silly:
Origin is for browsers/websites. The nobody would whitelist a particular
hostname.

Now that the server doesn't need Origin anymore, don't bother setting
one for clients. Users who need an origin can use DialWebsocket to
create a client with arbitrary origin if needed.

* vendor: put golang.org/x/net/websocket back

* rpc: don't set Origin header for empty (default) origin

* rpc: add HTTP status code to handshake error

This makes it easier to debug failing connections.

* ethstats: use github.com/gorilla/websocket

* rpc: fix lint

* all: simplify timestamps to uint64

* tests: update definitions

* clef, faucet, mobile: leftover uint64 fixups

* ethash: fix tests

* graphql: update schema for timestamp

* ethash: remove unused variable

spell correction from `repors` to `reports`

This PR implements the new LES protocol version extensions:

* new and more efficient Merkle proofs reply format (when replying to
  a multiple Merkle proofs request, we just send a single set of trie
  nodes containing all necessary nodes)
* BBT (BloomBitsTrie) works similarly to the existing CHT and contains
  the bloombits search data to speed up log searches
* GetTxStatusMsg returns the inclusion position or the
  pending/queued/unknown state of a transaction referenced by hash
* an optional signature of new block data (number/hash/td) can be
  included in AnnounceMsg to provide an option for "very light
  clients" (mobile/embedded devices) to skip expensive Ethash check
  and accept multiple signatures of somewhat trusted servers (still a
  lot better than trusting a single server completely and retrieving
  everything through RPC). The new client mode is not implemented in
  this PR, just the protocol extension.

* consensus, core, ethstats: use engine specific block beneficiary

* core, eth, les, miner: use explicit beneficiary during mining