Bitcoin-Qt: remove num transactions from overviewpage
Bitcoin-Qt: add wallet category and num unique tx IDs in dbg window

- this adds a new Wallet category to the debug window and implements a
  label which contains the current unique transaction ID count from the
  wallet (wallet model access is added to RPCConsole class)
- layout was converted from table to form and a spacer removed
- I also added an initialisation of the model variables in RPCConsole
  class, these were missing before