bitcoingui: show main window (if hidden) on modal messages
Merge pull request #3135 from Diapolo/bitcoingui

bitcoingui: show main window (if hidden) on modal messages
Qt: move paymentACK handling to paymentserver

- add new slot handlePaymentACK() to paymentserver, which handles
  paymentACK messages (currently we just display them)
- make paymentACK message a modal information dialog
- change some QObject::tr() to just tr()
- clarify the processPaymentRequest() error, when IsDust()
- small string change to prevent a tripple + usage with QString
paymentserver: init all class members in constructor
Merge pull request #3146 from Diapolo/paymentserver_init

paymentserver: init all class members in constructor
Merge pull request #3130 from Diapolo/paymentACK_via_message

Qt: move paymentACK handling to paymentserver
Merge pull request #3099 from laanwj/2013_10_new_receive_flow

qt: improve "receive coins" workflow
Added new config option noautofillkeypool.

One of the most annoying things about trying to maintain wallet backups is the fact that every time you unlock a wallet the key pool gets automatically refilled, thus making any existing backups of the wallet obsolete. The user now has the choice to disable automatic refilling of the keypool by adding the following line to bitcoin.conf:

noautofillkeypool=1

This effectively disables all automatic key generation, requiring the user to manually run keypoolrefill to replenish the wallet when the key pool runs low. It is recommended to call backupwallet immediately after calling keypoolrefill.

If noautofillkeypool is not set in bitcoin.conf, the app defaults to its old behavior thus ensuring full backwards compatibility.
Added ability to refill key pool from Bitcoin-Qt.
Got rid of the wallet default key since it isn't being used at all anymore and only produces bad behaviors in Bitcoin-Qt.