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/window/mainwindow/mainmenu.cpp

@@ -33,6 +33,8 @@
 #include "widget/menu/menushared.h"
 #include "mainwindow.h"
 
+OLIVE_NAMESPACE_ENTER
+
 MainMenu::MainMenu(QMainWindow *parent) :
   QMenuBar(parent)
 {
@@ -621,3 +623,5 @@ void MainMenu::Retranslate()
   help_debug_log_item_->setText(tr("Debug Log"));
   help_about_item_->setText(tr("&About..."));
 }
+
+OLIVE_NAMESPACE_EXIT