citra-qt: Add a utility spinbox class called CSpinBox.

This class has a few advantages over the regular QSpinBox:
- QSpinBox stores its as signed 32 bit integers, which for instance is unsuitable for representing memory addresses. CSpinBox uses 64 bit integers instead.
- QSpinBox does not provide an easy way to handle number input from bases different than 10.
- QSpinBox is quite inflexible in general and almost any sort of customization requires reimplementing it anyway.

src/citra_qt/CMakeLists.txt

@@ -11,6 +11,7 @@ set(SRCS
             debugger/graphics_cmdlists.cpp
             debugger/ramview.cpp
             debugger/registers.cpp
+            util/spinbox.cpp
             bootmanager.cpp
             hotkeys.cpp
             main.cpp
@@ -26,6 +27,7 @@ set(HEADERS
             debugger/graphics_cmdlists.hxx
             debugger/ramview.hxx
             debugger/registers.hxx
+            util/spinbox.hxx
             bootmanager.hxx
             hotkeys.hxx
             main.hxx