Slow account creation

[AndreMiras]

I'm using pyethapp for two cross platform apps and noticed from the beginning the account creation and unlock was very slow. In fact this is a follow up from ethereum/pyethereum#750.
This is specially more annoying on smart device because it has less resources and the user has to wait for ages to unlock account to sign a transaction. Up to a point where I had to decrease the security by lowering the number of pbkdf2 iterations.

In fact the fix should be pretty straightforward since the new eth_keyfile.keyfile.create_keyfile_json() implementation is way more faster. So I guess we should "just" pull the dependency and switch to that one.

Checklist

• [ x ] installed pyethapp inside a virtualenv

System/environment

• OS: Linux and OS X and Android
• python version: Python2 and Python3
• pyethapp version: develop 9af6e64
• installation method (pip & pypi/git & setup.py): git & setup.py
• pyethapp branch (if applicable): develop

Expected behaviour

Almost instant account creation on:

from pyethapp import accounts
accounts.Account.new("password")

Observed behaviour

Just super slow.

Steps to reproduce

from pyethapp import accounts
accounts.Account.new("password")

And cry 😢

[AndreMiras]

Pull request that fixes it #293