[Qt] additional small fixes for #3099 (new receive flow)

- remove 2 unneeded windowTitle attributes, which bloat our translations
- cleanup some unneeded .cpp/.h includes and class usages
- use a more generic string for clearing sendcoinsdialog and
  requestpaymentdialog
- edit 2 strings in BitcoinGUI and replace "edit" with "show" as this
  seems more clear in the context where it is used
qt: clean up signal handling in walletframe/walletview

Use proper signals everywhere.
Removes the need to store a pointer to the BitcoinGUI object in
the walletview.
Also removes the interdependence between setWalletModel / setBitcoinGUI.
Merge pull request #3151 from laanwj/2013_10_walletview

qt: clean up signal handling in walletframe/walletview
Merge pull request #3150 from Diapolo/misc

[Qt] additional small fixes for #3099 (new receive flow)
qt: english language update
Merge pull request #3165 from laanwj/2013_10_english_lang

qt: english language update