[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

src/qt/sendcoinsdialog.cpp

@@ -3,7 +3,6 @@
 
 #include "walletmodel.h"
 #include "bitcoinunits.h"
-#include "addressbookpage.h"
 #include "optionsmodel.h"
 #include "sendcoinsentry.h"
 #include "guiutil.h"