mobile: fix ropsten chain configs

This commit introduces a FindOnce method for filters. FindOnce finds the next block that
matches the filter and returns all matching logs from that block. If there are no further
matching logs, it returns a nil slice. This method allows callers to iterate over large
sets of logs progressively.

The changes introduce a small inefficiency relating to mipmaps: the first time a filter is
called, it acts as if all mipmaps are matched, and thus iterates several blocks near the
requested start point. This is in the interest of simplicity and avoiding duplicate mipmap
lookups each time FindOnce is called.

* whisper: refactored message processing
* whisper: final polishing
* whisper: logging updated
* whisper: moved the check, changed the default PoW
* whisper: refactoring of message queuing
* whisper: refactored parameters

accounts/abi: prepare ABI to handle fixed point types

Signed-off-by: VoR0220 <rj@erisindustries.com>

core: allow zero priced transactions from inexistent accounts too

internal/ethapi: fix hex handling for eth_sign, personal_{sign,recover}

p2p/nat: fix a bytes based net.IP comparison

p2p/discover, p2p/discv5: use flexible comparison for IPs

core: import future blocks one-by-one, enfore chain ancestry

VERSION, params: start Geth 1.5.6 development cycle

params: stable version 1.5.5

miner: clean up unconfirmed mined block tracking

cmd/swarm: one command  with subcommands

build: Ubuntu wily was officially deprecated, drop support

core: init pending state in tx pool on creation

cmd/utils, eth: Add gzip support for chain dump and restore

travis, appveyor: build with Go 1.7.4

cmd/geth: drop legacy android code

Miner race fixes