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/dialog/actionsearch/actionsearch.cpp

@@ -25,6 +25,8 @@
 #include <QMenuBar>
 #include <QLabel>
 
+OLIVE_NAMESPACE_ENTER
+
 ActionSearch::ActionSearch(QWidget *parent) :
   QDialog(parent),
   menu_bar_(nullptr)
@@ -251,3 +253,5 @@ void ActionSearchList::mouseDoubleClickEvent(QMouseEvent *) {
   emit dbl_click();
 
 }
+
+OLIVE_NAMESPACE_EXIT