Minimal architectural changes necessary to support multiple wallets in bitcoin-qt

- This commit is a minimal restructuring necessary to support multiple wallets in the UI. Please see multiwallet-qt.txt for details.

bitcoin-qt.pro

@@ -186,6 +186,9 @@ HEADERS += src/qt/bitcoingui.h \
     src/qt/transactionfilterproxy.h \
     src/qt/transactionview.h \
     src/qt/walletmodel.h \
+    src/qt/walletview.h \
+    src/qt/walletstack.h \
+    src/qt/walletframe.h \
     src/bitcoinrpc.h \
     src/qt/overviewpage.h \
     src/qt/csvmodelwriter.h \
@@ -250,6 +253,9 @@ SOURCES += src/qt/bitcoin.cpp \
     src/qt/transactionfilterproxy.cpp \
     src/qt/transactionview.cpp \
     src/qt/walletmodel.cpp \
+    src/qt/walletview.cpp \
+    src/qt/walletstack.cpp \
+    src/qt/walletframe.cpp \
     src/bitcoinrpc.cpp \
     src/rpcdump.cpp \
     src/rpcnet.cpp \