various: encapsulate all code in the olive namespace to avoid name collisions

Large-scale code cleanup. Also adds a license to the top of all files that were
missing it.

app/widget/slider/stringslider.cpp

@@ -20,6 +20,8 @@
 
 #include "stringslider.h"
 
+OLIVE_NAMESPACE_ENTER
+
 StringSlider::StringSlider(QWidget* parent) :
   SliderBase(kString, parent)
 {
@@ -46,3 +48,5 @@ void StringSlider::ConvertValue(QVariant v)
 {
   emit ValueChanged(v.toString());
 }
+
+OLIVE_NAMESPACE_EXIT