Add listAddressbook to api

listAddressbook returns label and address for each address in the
addressbook.
Use fast PoW unless we're explicitly a frozen (binary) version of the code
Actually OSX app maded with py2app can parallelize just fine
Allow specification of alternate settings dir via BITMESSAGE_HOME
Move duplicated sql code into helper
Have API calls use sql helper
Have bitmessageqt use sql helpers
Have helper_inbox use helper_sql
class_singleCleaner uses helper_sql
Merge branch 'master' into sql_refactor
use helper_sql for helper_sent
use helper_sql in class_singleWorker
use helper_sql in class_receiveDataThread
have shared.py use helper_sql and move the sql queues and locks to helper_sql
Merge branch 'master' into sql_refactor
new API method needs to use helper_sql
Fix regression where I couldn't add a subscription
Fixed regression in adding to address book
Merge branch 'master' into Fast_PoW_unless_frozen
Merge pull request #461 from Atheros1/master

Use fast POW unless frozen