IniFile: Make Section's string constructor instances take strings by value

As the name is immediately stored into a class member, a move here is a
better choice.

This also moves the constructor implementations into the cpp file to
avoid an otherwise unnecessary inclusion in the header. This is also
likely a better choice as Section contains several non-trivial members,
so this would avoid potentially inlining a bunch of setup and teardown
code related to them as a side-benefit.

Source/Core/Common/IniFile.h

@@ -29,8 +29,8 @@ public:
     friend class IniFile;
 
   public:
-    Section() {}
-    explicit Section(const std::string& name_) : name(name_) {}
+    Section();
+    explicit Section(std::string name_);
     bool Exists(const std::string& key) const;
     bool Delete(const std::string& key);