DefaultMediaTheme: move controls to a namespace

They have generic names and are likely to conflict with other things. In
particular, there is another BPrivate::TitleView in BColumnListView,
which results in weird behavior (and me wasting days debugging things
and scratching my head) when one links libmedia before libcolumnlistview
and the wrong one ends up being called.

src/kits/media/DefaultMediaTheme.cpp

@@ -34,6 +34,8 @@ using namespace BPrivate;
 
 namespace BPrivate {
 
+namespace DefaultMediaControls {
+
 class SeparatorView : public BView {
 	public:
 		SeparatorView(orientation orientation);
@@ -140,6 +142,10 @@ class DiscreteMessageFilter : public MessageFilter {
 		BDiscreteParameter	&fParameter;
 };
 
+};
+
+using namespace DefaultMediaControls;
+
 }	// namespace BPrivate